I will mention that Ruckus stuff in my experience delivers AC data rates to a much greater coverage radius compared to other stuff I've used. It might be worth it.
However, I've found that the 3-stream vs 2-stream (and degree of beamflex-ness) tend to be less important. Specifically, the R500 and R600 might give you excellent bang for the buck in 802.11ac land.
It is unfortunate the AC stuff currently doesn't Mesh, and I've previously asked (and didn't get an answer) as to when it would. If it's meshing that's holding you back, I would suggest 7982's or maybe 7372's even.
Especially if your clients are a bunch of iPads and the laptop bandwidth difference (33% for 2 vs 3 stream) isn't a huge deal, remember that iPads are 2 stream devices, and the price difference between a 2x2:2 and 3x3:3 unit (e.g. 7372 vs 7982) may not actually be worthwhile if replacement cost is an issue.
Overall though, as long as you don't rely on meshing, my personal opinion is that you want AC stuff, but you might want to wait until the full story on Wave 2 802.11AC comes out before choosing your next upgrade.
