Luckily most of my $400> purchases I've been able to try before buying, either by demo or loan. I consider $300> purchases without hearing a product a recipe for suicide. Because I've heard some real shockers, even to the point questioning if they were faulty. Heir 3Ai was one of them the orginal ASG-1 V1.2 another Luckily they were only demos. if I however I paid full price and put them in my ears I'd be absolutely gutted. That's the beauty of mid-tier, you can try products (some very capable) without feeling like someone just sliced your testicles off if it doesn't work out. I think my expectations are rather high though, I bought a pair of Beyer DT1350 which arrived today which haven't won me over yet although the Beyers are decent, theres some real crappy over priced gear out there.
Sell 'em and get the M500's :)
Everything else you said it true though. There is no way I would pay >$300 for something without auditioning it first (unless I thought I could return it or for sure sell it without a major loss).