I'm in favor of a new map. Part of the reason I haven't played in the past few weeks is that the feeling of adventure and discovery was starting to dwindle. A new map and new features would for sure get me playing again. I'm actually about to head to the beta server and check out the new stuff.
I think I'll enjoy playing a version where we have no stargates or /home to rely on. Hell I used /home more as a way to escape danger than anything else. Like others have suggested, I think the lack of instant teleports to the far corners of the map will encourage more of a community type environment. A minecart network would be more fun to travel than just insta-teleporting places. Plus once (if?) the nether starts working in SMP, we will have that option to travel farther distances quickly, with the element of risk mixed in.
It's going to suck not having infinite diamond tools and infinite lava generators, but we knew all that was going to come to an end eventually. And besides we can't stay in alpha forever. For all the "good" features we keep by staying in alpha, we are missing that many more new and fun features beta has to offer.
tl;dr New map for beta!