Even if you don't want to use Google+, why can't you think of it as just another account you have to make. Imagine Hangouts was a great stand-alone product made by a start-up. You'd still need a whole different account to use that stand-alone Hangouts product.
So I'd suggest just looking at it like that, if you really don't want anything to do with the whole Google+ part of Hangouts. Plus, it looks like Google wants to make Hangouts work in more of their services than just Google+, and I think that's a great idea. They could probably implement Hangouts in a lot of their other products, to get people to "video socialize" around them, and maybe build fun ways to use it with those other products.
And agreed about the G+ relationship - happy to see it moving into gmail.