I like the idea of rotating between east, west, and central locations. At least until we get a sense of what works and produces good turn-out. I don't think we should do it more often than say every 9 months. Local meet-ups are one thing, but we want KeyCon™ to be special. I'm also totally down with paying to get in if it means better venues and more interesting things to do and see.
If we were able to pull off a big event every year, that would be quite a feat. Attempting to do two per year is overkill.
One annual conference would be easier to plan for (both for organizers and for the attendees) and easier to get vendor support if we're only hitting them up once a year. I really like the idea of rotating the location though. This year was Chicago, next year California, and then 2015 is in New York, for example. For the conferences that I participate in for my day job, that's what they do both on the State level and the National level and it works quite well.
We should be planning at least 9 months out if we're doing a "big" conference, so to do more than one per year is a big commitment to whomever is planning it. Why? Because you'll be constantly planning as they will overlap. You'll be running the spring conference while trying to commit people to the fall conference. That's a lot to ask.
I know there is a lot of excitement over the first one and we're all eager for another (myself included), but I think meet-ups will work better between conferences, rather than attempting to do two conferences per year. Not to mention that I love how laid back and relaxed a meet-up can be. It's a whole different vibe and much more one-on-one than a full Con.