2002 Bonneville--vibration during acceleration

Please forgive the length, but it is necessary. I have a 2002 Pontiac Bonneville SE, 3.8L engine. The car currently has 123K miles on it. Since 2005 I have been experiencing a moderate to severe vibration during moderate to hard acceleration, and I would like to better diagnose it so that it can be repaired. Oddly enough, the vibration is more severe when more weight (passengers) is added to the car. Here is a brief history on the vehicle. During the first winter after I purchased it in 2002, I accidentally hit a snow-covered curb at 40mph with my right front tire. The impact dented the rim. I had the local Pontiac dealer inspect the car for damage and all they came up with was a dented rim. There was some slight vibration at highway speeds, but I & the dealership attributed it to the rim, and it is nothing like what I am experiencing today. In January of 2005 I had to replace the wheel bearing for this same tire. Then in May 2005, while on vacation driving in Florida, the vibration started that I am asking about (at this time the car had about 85K miles). It started suddenly and without any obvious cause. The vibration was severe, and it felt like I was hanging onto a jackhammer. At first I thought it was a tire out of balance. But after several rotations & tire balances (even at a Pontiac Dealership in Florida), the vibration persisted. The vibration was so bad that it gave each tire that was rotated to the front of the car a visibly uneven wear pattern (I had to replace the tires later that summer). It wasn’t until I returned home (after driving over 1000 miles with this vibration), that my home dealership found that my right front boot was ripped and the CV joint was damaged beyond repair. They replaced the right front drive axle assembly (notice the reoccurring maintenance on the right front tire). The vibration diminished some, but has continued & progressively gotten worse to this day. I have discussed this with my dealership, and they cannot offer any concrete answers. They told me to drive it until it started getting worse. Since the vibration is only felt during acceleration, the dealership is convinced the cause of the vibration is in the front axles of the car. They say they have no vibration sensors for diagnostics, so they are unable to determine which side. They are quoting me $80 to remove the axle assembly they installed for a visual inspection to see if it is binding, and $300 for a new one. Here are the questions: what could be causing this vibration? Does the dealership’s diagnosis make sense? Do the prices seem fair? And finally, does anyone know of a way to detect vibrations to determine where it is coming from?

Thanks
Zach