07-14-09: Shadorne
Better YES. Practical NO. Of course it is better but it depends on how willing you are to invest for the small amount of 7.1 soundtracks available.
For me, having a 7.1 source on the soundtrack is nearly immaterial. My AVP can matrix 7.1 from any 5.1 source, and does. It fills in the back and provides a more enveloping sound whether coming from a 7.1 or 5.1 channel source.
7-channel sources are growing rapidly, as just about anything coming out on Blu-ray these days is 7.1. The true 7.1 channel sources *do* provide more discrete rear channel specificity, but even in a matrix where the rear surround channels are only playing the signal common to LS and RS, it still fills in a gap that otherwise occupies the rear third of the room.
If you already have a 7-channel AVP or AVR, the additional cost of rear fill-in speakers and a pawnshop amp is minimal (e.g., I got an Adcom 535 II for $75). The only potential hassle is laying the front-to-back speaker cables.