Should I buy this horse?

As a project horse? Definitely, she sounds really cool and challenging for an experienced handler (which it sounds like you are). Smart move not making her a kid's horse, and whether or not she'll ever be able to do anything along the lines of competing is pretty doubtful, but if you have the money to care for her, then why not? And you never know, she might end up shaping up into something great. I have a half-draft, and I completely love her, so maybe I'm a little biased. :)