I am with Hilltowner on this one for the most part. I have the original Grand Bois Hetres on my bike and they certainly transformed the bike. Supple tires make the world of difference. With that said I don't I use them for commuting because they aren't flat resistant, for that I use Schwalbe Marathons. They ride like crap but I am not fixing flats all the time and getting to work is more important than having a more comfortable ride.

I am not convinced you need to change your bike, if it works mechanically then change your tires to something more supple, lower the pressure to help absorb the road shock. Spending $150 on tires on a $100 bike is still cheaper than buying an unknown condition $300 bike.