I would say it is worth the wait. I'm sitting with a N1 right now and waiting for the Galaxy S 2 to come out to see what that's all about. However you can go ahead and get a top tier single core phone right now, they aren't going to be replaced anytime soon.A problem that I have is that the Optimus Speed is still not available in my e-plus and BASE shops... you think it could be available by May? If not until then I'd take the Arc or SGS...
Is it worth the wait if you need a phone for the next years?
I predict that single core, 1ghz phones will be around for at least this year and next year; at the end of 2012 is when a dual core phone should be a... good incentive on getting it. (Spec wise anyway).