Every single time I have been at BLT, there has been plenty of parking available. And yes, I also have been out on my balcony watching people drive in and park, then walk over to MK. I have watched people walk to their cars at park closing, and get in and drive away. They seem to take the spots closer to the MK though....not spots we would actually be using if staying at BLT.
I do think that every deluxe resort (that has direct park access) should have room key activated parking gates!! Just like some of the pools. There could be a smaller lot for those checking in or just 'visiting' the resort. A receipt could be given out to those people using the short term lots...if they returned, within 3 hrs, they get parking free. If they don't return, they are charged $15. Seems pretty simple to me. Sure would alleviate all these 'discussions'!!
And that system seems to work at the US/IoA resorts!! But they charge a per day fee, even for resort guests!! I don't see why a similar, but free for those staying at the resort, couldn't be implemented at WDW.