I did 100% of my IFR training in a 152; and I had a blast.
I saved a very decent amount of money doing it that way; which is good because it was really the only way to do it with what I make...
The training was fantastic, and we definately sought out actual as much as we could. It does get bumpy but IMHO 152s are built very strongly, and the point is training: if you get the experience of being rocked in a 152; the bumps won't feel so bad by the time you 'move up' to the 172.
I definately see where you guys are coming from regarding icing and climb performance. Basically if there is any chance of the freezing level getting near the cruise altitude we don't go, which isn't too hard even in winter.
I should mention two distinct memories of my training: having to pull the power waaaaayyy back, and pitching down just to maintain altitude. The updraft was around 1400fpm which would do the same thing to any plane; just that the 152 responds to it faster. When you go up... you go up. The other time was having full power at Vy and barely hanging on to altitude. We were VFR and definately in a downdraft. Got out of it in 30 sec or so and were on our way.
The other consideration is the fact that you don't have much airspeed to play with during cruise. It actually cruises below Va, which is nice sometimes, but if you pull the carb head and go full power you'll only get 75-80kts, or about 10kts more than Vy. Get some ice and you're descending, no question about it.
As for overall climb performance... it wasn't so bad. On one flight we went up to 9500' and were climbing at 300-400fpm, and every one of our flights was right up at max gross (this was with a 110hp stock 152).