This is what I'm talking about! The difference between both are not that great unless you need to get deep and large and I'm not too sure I really need that.
I've owned both and I like both.
X18 is an awesome mixer with tons of features for the price.
That being said, I sold the X18 and got a second (and third) X32.
These are the features that (after using for a while), I felt I needed to have (and the X18 doesn't have them).
1) True Xover filters. - X18 only has Eq on outputs, I use the X32 for its Xover capabilities, and it's excellent at it.
2) Matrix mixes - this is amazingly valuable to me when I need to tap into an in house PA with my Mixer.
3) DCA groups (similar to a subgroup on an analog mixer). You can get these with the droid version of the App, but not on the iOS version (fader groups are not as clean and easy to use).
4) I LOVE having he layers within the iOS app. It allows me to set one layer to have 4 DCA (sub) groups and 4 Monitor sends...which means I can make any of my major tweaks to the mix, from one screen (with only 8 faders).
5) Expansion card in the back (X-Live) which allows 8, 16 or 32 track recording to a SD Card. I track most gigs and leave with full multitrack files...in my wallet. Zero extra equipment/effort to track a gig that I can mix at home.
6) X-Live allows virtual sound check. Record the band playing. Everyone leave the stage, play back the SD card and tweak the eq on whatever (ok, this isn't really useful to me, but it's cool knowing it's there).
7) Saved he best for last - FRONT PANEL CONTROL. In a pinch, I can mix from the front panel. I carry a spare router, but you still never know. X-Air, you definitely need an external router, but even then, if you can't connect for some reason...you're f'd. I've seen it. Full room, my buddy had an X-18. Didn't listen to anyone who told him he needed an external router. The room filled up (300 people), and he could not connect a single device for the rest of the night. Hope you're happy with your soundcheck mix, because you're stuck with it!!!
Chris, I also use the X32 for my rehearsal/studio interface. Works awesome.
As I wanted slightly better preamps, I bought the Midas DL16 (same form factor as the Behringer S16, but with true Midas Preamps).
I bought a X32 Core and that Midas DL16 for $1100. True Midas rig in a 3 space rack case. I keep that one in the studio.
I'm still watching out for a X16 on Craigslist, to keep in my car for emergencies. They are excellent mixers.
But if any of those features above are must haves for you, then you may want to dig deeper into the X32.
It's too bad you didn't live on the east coast, I'm always happy to give a quick start tutorial to anyone getting started in the X32. Makes that learning curve really small.