If you're talking about California vs New Jersey, sure, but there's quite a few people that go to both SFDK and SFMM, and having your pass processed at SFDK isn't a big deal, especially if it's a membership and you won't have to renew it each year.
I believe the SFDK pass is currently a little bit cheaper than SFMM already, but at the moment I don't think it's enough for MM to really care, I just wonder if they will care more if the disparity becomes larger.
I'm in Chicago, and I've known people to go St Louis to get passes (about the same distance as DK and MM). Personally, it seems unlikely to me they'd change anything - Magic Mountain already had a much longer schedule than a lot of the other parks for a very comparable price, would they really try to raise it enough to make this an issue just because they added a lot of days that most people won't use anyway?