I updated to a from a 2001 929 to a 2003 954 at the start of the year.
At first there did not seem much difference in the two bikes.
The riding position was slightly lower at the front, but not enough to cause any concerns.
I feel the comfort (or lack of it) is similar on both bikes.
The brakes feel a little stronger, but not heaps
The bike seemed to steer a little quicker, but i did not have a damper on the 954 at first, so that may have affected the outcome
At first the power did not feel that much different, but after about 4000 klms the 954 had loosened up and it definitly has more mid range.
The 954 looks more modern than the 929 does, but that's just my opinion.
The price difference probably wouldn't justify the update, unless you just want to get a newer bike, but if that is the case it will be superceded in a few months anyway. If you can get a 954 for the right price, just go out and get it