Sometimes you just have to rip it out

I completely unraveled 2 scarves I was working on. Both are supposed to be gifts; one is knit and one is crochet. They were going ok, but not giftworthy. I decided that I can't knit to gift quality yet and that I was using too small a hook for the crochet one. I've started both over as crochet projects (with appropriate size hooks) and they're going much better now.

I also have a project I started a while ago that I'd like to finish - but it would require purchasing more yarn. I basically just started crocheting with this pretty cool yarn; I realized after a while that I was making an afghan or throw of some kind. Except I don't have enough yarn to finish it. So my dilemna is whether to buy the yarn in order to finish the project that's going the best right now or to put that project on the back burner for several months until I work through some of the other projects.