hi, you made some interesting points in your post. personally i really like w7,[ i didn't try vista after all the bad press]. i had in fact left windows xp, to use linux but w7 has brought me back! i think w7 is going to be the OS that microsoft always hoped vista would be.
i have tried both the beta and rc versions and in fact have ordered the home premium at the low price. ultimate is available now at amazon although only at a measly £30 cheaper than the official price [£229]. i suppose microsoft were being generous with the home editions, but not that generous when it comes to the more expensive versions!
as far as i know w7 is only at the moment being offered as a fresh install, so you're idea of using a second hard drive is a good one. i installed the beta over xp, and the rc on a new fresh hard drive with no problems.
although one thought has occurred to me, when w7 is due to be released, there should be lots of pc sellers with a glut of vista machines. so hopefully there might be a few bargains to be snapped up, which then could be converted to w7, assuming you can get a version at the lower price.