Andrew M
I don't hold a PPL (hoping to start very soon though) and I wouldn't feel comfortable spending my money flying in an aircraft that doesn't teach me some of the fundamentals to flying other, more regular aircraft. Considering most schools/clubs still use Cessnas and Pipers on Avgas for their hire aircraft, then I would be at a disadvantage.
Point taken, BUT (and I say this only partially tongue in cheek) have you considered that you might want to get some serious utility out of your flying one day? If so, consider the reaction of a bird (a girl!!) which you are trying to impress, when she is
1) getting into a 1971 Cessna 150 (which to most people looks like it won't make the next flight, but they don't mind getting in because the instructor will die with them, and they assume "he doesn't want to die, so it will probably be OK")
2) getting into a new DA40 (which looks like a serious SEXY plane, a bit like the sort of car etc she is accustomed to)
??
The unfortunate reality is that in the eyes of most of the general public, flying small planes (great fun) and spotting small planes (rather sad) are two activities which are rapidly converging. Soon, the CAA will need to hand out an anorak with a new PPL. I believe this is the main reason why fewer and fewer people are learning. There's plenty of money about (stand next to the M25 for 30 seconds for example) so that's not the problem. The sooner the business gets away from flying decrepit old junk the better. The rest (diesel engines, FADEC, etc) are of secondary importance.
Incidentally, if I was running a school with a fleet of DA40s, with in-warranty planes, guaranteed buy-back deals and diesel fuel I could match the hourly rates of the 1970s Cessna outfit next door. I would train in the the DA40s, and they would be available for self fly hire afterwards, so the issue of type conversion to WW2 technology would be a non-issue for (mostly local) pilots.
A really smart school would sell aircraft shares to the more keen pilots, and when enough shares have been sold in a particular plane, that plane could be detached from the school and the school can then buy another one, brand new of course.