IMO, if you can't afford a regular copy of WinXP Home or Pro, then yes, it is feasible to use the 64-bit beta as your main OS. But if you already have a copy of regular XP, I would do a dual boot to have access to both at all times. If you do decide to use the 64-bit beta as your main OS, be warned that not all 32-bit programs will work with it, and you may have trouble finding some drivers for your hardware (not as much anymore). But it should be stable enough for a regular home user who just browses the internet and does small tasks like word processing and the like.
As for having new features, I don't think the 64-bit version will have anything new that stands out. I believe Microsoft is tweaking a few things, but I'm not sure of specifics. If you are a regular average joe user, it will most likely mirror what the 32-bit XP is now.