I find the last 5-6 months a lot more interesting than 2 years ago, but for what it's worth, there's been a steady increase for PSP going back to 2004. Hell, just look at Cup this year, it's looking like PSP is going to sell out 120 XBall teams by the end of next week with tons of demand on top of that.
As for XBall vs. 7-man, I've spent a LOT of time analyzing the relative costs, and I have a LOT of guys on my team that have all done budgets for both XBall and 7-man and 5-man and they've all come to the conclusion that XBall is at most marginally more expensive but definitely brings incredibly more value for the player's dollar than the other formats.
The price difference is especially not very significant at the national level - you have to start a day early, which adds an extra day of staffing costs, but that's fairly minor when you consider the portion of the total event costs devoted to having refs and grounds crew for an extra day. You don't have to build any more fields, for example. You also get some of that back by being able to run 5-man on the weekend. All in all, it's a bit more expensive, but revenue from teams for PSP is higher, and the number of players at a PSP event is higher as well.
It's also not more expensive for the players on a per-player basis for full-on XBall, nor on a per-team basis for XLite. Yes, if you play more, you shoot more paint, but paint is also such a small percentage of event cost when you factor in airfare, hotel, rental car, entry fee, etc, that once you've paid $500 to be there, if you can pay $100 more (xtra day hotel, rental car, food, and a case of paint) to double your play time, you'd be an idiot to not pay it.
Remember, total expense and VALUE are not necessarily the same thing. XBall may be slightly more expensive (a little more paint, some more staffing costs) but you get a LOT more bang for that buck. People are going to these events to actually PLAY paintball, right?