I've had a TDM900 for about 8t0000km before I got my first Tenere. It is a truly great bike and much underrated by the general motorbiking public.
The engine is a thing of genius, the chassis would not be out of place in a modern crotch rocket and the Sumitomo brakes go excellent feedback. I liked those so much I retrofitted them on my track TRX as well.
It is true the suspension lets it down a bit. That can be helped greatly by changing the spring on the shock and adjusting rebound and compression settings. On the front I changed the springs as well and used a slightly thicker oil. Once you get it right the TDM can take on any racer in the twisties.

I'm not sure whether the Tenere forks would fit. But what rim would you want to use? With the Tenere 21inch I fear the TDM would become a little slow to turn in. It already has a slight understeer, which can be more or less remedied by pushing the front forks through the top yoke about 10mm.
Also, make sure the airbox valve is disabled and plugged. It helps with the Euro3 flat spot Yamaha introduced around 3000-3500rpm.

There's a great deal of info over at http://www.carpe-tdm.net/ipb/