There is not that much difference between the SP1 and SP2, there was only 7 months between them, after all. It's really just a processor update, which brings better battery life (same battery) and a very modest performance bump. In the real world I think you'll only notice the battery life benefits. As Ken says, they did also gave you the option to order more storage inside it: SP1 was just 64 and 128gb, the SP2 comes with 256 and 512 options (as well as the first two) and those bigger capacity options come with extra RAM - 8Gb instead of 4gb. My 128Gb SP1 with 4gb RAM works great, and I'm not upgrading till SP3 comes out, probably in the Fall.
If you really are someone who goes off into the wild without power for multiple days and need to work tethered sometimes, then the extra battery life is worth it. If not, then I'd question the $1000 extra to get SP2 over SP1, as everything else is the exact same. I have never run out of battery power in a year of use with SP1 in the city, though it has a got quite low on two occasions.
Those differences aside it seems Microsoft have a sleeper hit on their hands as Surface Pro (not the regular 'Surface') - was on back order for a long time, and impossible to find over Christmas. Everyone wants the latest and greatest, so you can pick up the first version - like a 128Gb SP1 on eBay for $450 or so, in mint/ new condition, and for that money, its definitely worth it. Remember its a fully functioning touchscreen laptop-tablet too, so you can watch Netflix, Hulu, surf the full internet with Flash, and do image processing on it if you want.
That said, this is MF digital, and everyone here seems to buy the best, latest and most expensive of everything, so who needs to save $1000? I'll probably be kicked out for suggesting such heresy.