I imagine there is some crossover audience for both festivals, and some people who would like to attend both, but have to pick only one due to financial reasons.
To build on what a couple of people have suggested in posts above, if worse came to worse, perhaps the two festivals could alternate years. Each festival would then be a bit more rare and special, and it would make it easier for the core audiences to attend *both*.
I was somewhat surprised that I don't ever recall hearing of NEARfest, even though it has been around so long and is only one state away from where I live in Maryland.
Then I looked at the previous line-ups and realized that it seems to be mostly a prog rock/metal festival. Of all the bands listed in their past line-ups I recognized maybe five or six names and was really only interested in two (Porcupine Tree and Glass Hammer). Granted I've never heard of most of these bands so I could be totally off base on where they are at musically and if I would like them or not.
I like some prog, some death, but I'm generally more of a power metal girl. I am very happy with the ways PP provides a fairly even mix of these types of bands (some pure power, some pure prog, some that blur the lines, and some that push the boundaries of these two genres a little more in other directions - AOR, death, folk, etc.). I'm not opposed to the occasional growls, heavier bands, or progressive bands, but I would not really want PP to shift drastically in any of these musical directions.
Regarding the idea of these two festivals combining in someway ... As I have said, I do not want PP to become more predominately prog but remain a mixture of both prog and power metal. I would also prefer that these festivals not alternate every year. I like PP as an annual thing. If alternating years was the case, I would probably just end up going to PP every other year and not going to NEARfest, unless NEARfest decides to change the style or caliber of their bands in some way to include more bands (or metal styles) that I am familiar with.
Working together is one thing, but ultimately, I don't think that changing the style of either festival would be good for the respective festivals' current fanbases.
The biggest reason I come to PP is because there are generally at least 3 or 4 bands that I'm really interested in and I can generally guarantee that there's going to one or two bands that I know very little about that blow me away once I see them live. Sometimes there are more bands like those. Whatever I don't care for as much, generally allows me the time to do merch, food, and meet with friends.
Which leads me to another big reason I come to PP is for the company and the "experience." I have never come just for a headliner and this year I don't really care about either of the headliners at all. If I really love half the bands on the bill that's still incentive enough for me to go. The "undercard," the good mixture of bands, as well as the company, is what really draws me to PP.
I would be a shame to see PP burn out or fade away. I hope it can continue for a long time, but I also believe it's called
Prog Power for a reason. If you're going to do something way different, than I'd rather just let PP end on a strong note and do a different fest under a different name.