I'm not a pro by any means, and tend not to be a super pixel peeper, and have found DX works pretty well for my needs. When I finally (rather late) went to digital, I got a D3200, largely for cost and portability, and have used it a lot in the last three years or so with rewarding results, except that I have been annoyed by high ISO noise and the cheesy viewfinder which makes manual lens and macro work difficult. I recently graduated to a D7100, which is nicer in many ways. But I was always surprised by how good an image even the lowly D3200 can produce under the right conditions.
My main motivation for getting a full frame camera, if I did, would be the relative ease of getting wider angles and shallower depth of field, and the relatively better viewfinder. As a secondary issue, because I have a lot of older lenses, it seems as if it would be a nice thing to get the fields of view they were originally good for. But I'm finding I'm in no big hurry for this. The ability to use older lenses, even if the field of view is different, is a feature I really like.
Of course this will vary with what you do and how you do it. I travel a good bit these days, and need something light, and also not so valuable that it would break my heart to lose it. I try not to have to check any baggage. The D3200 with cheap lenses is a perfect traveling rig for me, and the D7100, though a bit bigger, is still in the running.
If I were a wedding photographer or worked in a studio, I'd likely choose differently.
