My opinion, based on my experience and some of what I've read, is that the only real purpose of those "power conditioners" is the surge protection that they provide. So, if you already have good surge protection, then I would say that you certainly don't need to spend another $500 on the Panamax.
Some people do claim to get audio and/or video improvements with the conditioners. If your power is bad enough, then I believe that is possible. I didn't notice any differences (nor did I expect to) when I replaced a Panamax surge protector with a Belkin power conditioner - I just bought it because I liked the looks of it better and I needed a few more outlets.
With Best Buy, you could always buy the Panamax, try your system with and without it, and return it if you don't see any differences. Just make sure that they aren't going to charge you a restocking fee.