I have a Platinum from San Diego. I started it on EZ Pay in 2011, I think, and my payment is a mere $10.66/month. I will never give it up!
As far as I know, it has to be activated at the home park. I had to get a new pass at one point because mine was damaged, and they mailed me one from San Diego (I explained to them that I used to live out there, but moved to FL, and they were happy to help). They told me in Tampa that they weren't going to be able to reprint my pass there, but they were able to let me in. However, they also had no issue transferring my pass info to one of the $5 Guy Harvey plastic passes in Orlando, so I have no idea if that was true or not.
I have gotten the same benefits in Tampa and Orlando - they always give me preferred parking and the same discounts. The only snag we've run into is when my wife's received free Quick Queue passes for new attractions at her home park (she has a pass from Orlando), but I'm unable to obtain the same benefit.