Wow - I haven't been here in a while.
There are a lot of good suggestions here. My advice is to just play as many guitars as you can and when you find the right one you'll know it. That sounds like a cheesy sentimental plan, but it's absolutely true. Acoustics in particular vary tremendously from individual instrument to the next. One Martin D-28 may be perfect and the next one's a dog. (It's not necessarily a quality control issue, just an individual piece of wood issue.)
Play used guitars, too. The last acoustic I bought was a 1936
Gibson L-00. I wasn't in the market for a guitar and couldn't afford it. It made me pick it up. It made me sell one of my favorite electrics. It made me buy it.
I have no regrets. I would have hated myself if I never bought it. Apart from being very cool, it sounds amazing and is the most lively instrument I've ever played.
The only guitar I have played that has come close for me is a friend's mother's Martin D-35. I've played other Martins and never has one sounded as good as that one.
Another brand to check out (though probably in about the same price range as Martin) is Larivee. The last time I played a whole bunch of acoustics all in one day, a $1500 Larivee was far the best, even comparing it with other guitars (Larivee, Martin, Taylor, etc.) $4000 and up. Of course, that wasn't the store where I played the $5000 Goodall, which was mighty fine, too....
