If you make a list of how exactly you want your plane to be, you end up creating a company and producing your own aircraft. And in 95% of the cases you go bankrupt 
Yes; the TB20 is very very hard to replace.
I love watching you Socata fanboys in action! 
The SR22 does nothing which the TB20 doesn't do, in terms of mission capability, if the same equipment (e.g. full TKS) is or is not fitted.
Obviously it is more modern and if you want a new plane, the only option of those two.
A move TB20 to SR22 is pointless, unless you just fancy something different.
I love watching you Socata fanboys in action!
You should read some of the stuff on the Cirrus user group
The SR22 does nothing which the TB20 doesn't do,
Fly faster than 200 knots? Land vertically?
For a lot of people with money only a new plane is attractive, same as with yachts. The interior of the Cirrus G5 is very slick, the TB20 looks like a 1980 Renault...
The main difference in mission capability is that your safety margin in hard IFR is much higher due to the chute. Departing in zero visibility with a TB20 or even those flights over foggy terrain bear a much greater risk in the TB20 than in the Cirrus. I consider a Cirrus to be superior to a piston twin in safety.
PS: The mission capability of a 2013 Mercedes E-Class station wagon is about the same as that of a 1970 Volvo station wagon only that the number of people pointing out that fact and driving the 1970s Volvo is rather small compared to the buyers of the 2013 E-Class...
Peter,
people who know me know that - although I have operated a Cirrus for 13 years now - I am not one of those fanatic Cirrus owners who just say "there is nothing else".
However, your point about the TB20 being hard to replace is IMHO off the mark, because the SR22 is and has been the market replacement of the TB20.
BTW, I have also flown the TB20 extensively. And I have stated myself that the TB20 does indeed represent a rather nice blend of qualities. However:
An SR22G3 will do everything the TB20 can. Does it perform significantly better (other than cruising faster at the same fuel flow)? Probably not, but certainly, it does at least what a TB20 does.
A 2008 SR22G3 will sell for 240000 Euros - not much more than a 2002 TKS and otherwise fully equipped TB20 will cost.
Range, when flown as conservatively as you do, at least on the G3 model, will be about the same (roughly 1100-1150NM plus reserves).
Cruise, at FL110, is 170 knots at 12.5 GPH, or - if you like it - 160ish on 11 GPH.
Initial climb rate (at MTOM) is 1200FPM at 130knots. Climb to FL200 feet is no problem.
The Cirrus has more room in the cabin.
Payload at full fuel will be about equal (200 kgs). Remember the comparison is with a TKS equipped GT model.
I would say the reason Socata stopped the TB20 in 2002 was Cirrus starting to deviate customers from them. And: they realized that the market was too small for two manufacturers to make money out of it.
I consider a Cirrus to be superior to a piston twin in safety.
Cirrus has for many years been plagued with one of the worst safety records in GA.
Also, you will have a window where the chute can't help you under those conditions you are describing.
The main difference in mission capability is that your safety margin in hard IFR is much higher due to the chute.
I agree that it gives you a way out if the engine quits in the conditions you are describing. However, the accident record shows that the Cirrus is not a safer airplane than the average piston single or piston twin.
You can find numerous articles about this on the web. Here is a quote from Richard Collins "Despite all this, the Cirrus SR-22 has a higher fatal accident rate than most similar airplanes from other manufacturers."
The article is here
Of course you can "replace" a TB20. Plenty of planes will do the same mission with similar safety. For example an SR22 will replace a TB20, and if you are happy with something 30 years old then the field expands hugely.
An objective go/no-go decision, given the basic "250-300HP IFR tourer formula" hangs on equipment for equipment. A TB21 with TKS will be similar to an SR22T with TKS. But a TB20 with TKS will totally outclass any SR22 without TKS for frequent-flying winter IFR.
In reality it is less black and white, because different people have different attitudes to risk. I know people (including some TB20 owners) who practically always fly. They fly through any frontal weather. One of them collected 3" (75mm) of ice on the leading edges, once. I know from my ice "tests" that he was going down, but evidently (he is still here) it came off before he hit the ground. He probably started at about 10000ft and -5C, which would work OK. Personally, I do very little ice and do flights more or less only if the enroute section can be done VMC; FL200 if necessary. That also makes it comfortable for passengers; TKS might protect the plane but the ride in some TCUs could be interesting...
There are also differences in ice carrying ability, and legend has it that the SR22 and the DA40/42 are very susceptible to ice, compared to planes with thicker aerofoils.
The rest is detail e.g. yoke v. sidestick, etc. It doesn't affect what the plane will do with a given level of safety.
The SR22 BRS chute would allow one to be more comfortable flying at night or over mountains, but the engine failure stats (failure followed by an "impossible" forced landing situation which unavoidably caused the plane to be wrecked) do not really feature in SE fatal accidents. If they were big, SE GA would be dead.
Most SR22 chute pulls were not irrecoverable landing scenarios. Some were positively comical in the ample choice of landing surfaces. Some were ridiculous in the preceeding risk management. Even the one where the aileron came off was not an unflyable plane. In most of the chute pulls, the pilot chose to pull the chute because it was there, which is fair enough.
That AIRFACTS article does resonate with Cirrus marketing; some sort of correlation would be expected.
The rest is detail e.g. yoke v. sidestick, etc. It doesn't affect what the plane will do with a given level of safety.
IMO a few of the features that Cirrus has are more than just details.
The side yoke with its spring load system I believe is unique for a piston single. That feature has a rumour of not providing a lot of feel to the pilot, especially at low speeds. Maybe the Cirrus pilots can clarify.
Also, the single handle throttle system (plus mixture) is not found in any other pistons. Some love it, others hate it.
Anyway, the aviation marketplace has spoken and appointed Cirrus a clear winner within GA.
Personally I would rather fly an older Bonanza, TB or a Saratoga for the same money (ca €150k-€200k) that buys a nice Cirrus.
However, your point about the TB20 being hard to replace is IMHO off the mark, because the SR22 is and has been the market replacement of the TB20.
I guess that Peter's comment on TB20 not being replacable was mainly directed to me and I read it like "if one ownes TB20 it's hard to find a replacement for it".
OK let me re-phrase it once more: it's hard to replace a TB20 with something that delivers a worthwhile mission capability improvement, without spending a whole lot more money.
I consider a turboprop to be the next step. An SR22 (or almost any other SEP currently out) is just a step sideways.
It's true that a Cessna 400 goes a lot faster
(one I flew in) but also at a much higher fuel flow, and by the time you throw in the eye watering purchase cost, you may as well go for a Jetprop which will outclass it completely. I suppose I am not the only one who thinks that, since C400 sales are hovering close to zero.
This is the problem with pistons... there isn't much of a progression above say 150kt. You can get 170kt but the fuel flow increment is considerable, and then you can get great TAS figures at high altitudes which don't make sense if flying unpressurised with "normal" passengers. I use oxygen all the time (Euro IFR would be all but useless without it, to me) and would not want to do it above FL200.
