Ok...let me make this as simple as I can. I sat out on my BLT balcony, on multiple occasions (early morning, early evening), and watched as security people either walked or putt putted in their little cars, around the BLT lot. They wrote something down on their clipboards, especially in the late afternoon. I 'imagine' that they take note of cars without those dashboard placards and then check to see if they're still there later in the day. In addition....I have asked security (in my capacity as a moderator for this board, in an effort to get good info) if they take note of cars without resort id on the dash. Yes, was the answer. And that they will take action if it's a busy time of year! So, while you may get away with it in late August, you may not get away with it during a holiday season.
I also own DVC at BWV. If you want to watch something entertaining, sit out and watch the parking lot at 9:45ish. What was a fairly full lot becomes a ghost town..with a ton of close up parking available. Why? IllumiNations just ended! There are a ton of people that drive to BW, self park and then head to Epcot. The line of cars seen exiting the lot is incredible on some nights. Of course, people will tell you that 'Oh, I just want to avoid the huge numbers of cars exiting the Epcot lot'...well, so does everyone! And when you pay a lot of money to stay at a resort, with park access, and you can't find a place to park when you return around dinnertime? Yep, it's frustrating...because you know those spaces are taken by guests who are not staying at the resort.
Sure would be nice if there were to be smaller lots available to the public, with the larger lot key access only. That way, those wanting to eat/shop at a resort could do so. They would get free parking for up to 3 hrs. After than, there's a charge to park! You could even do that without blocking an area off. Everyone that went in, without a room key/MB access, would get a parking stub. Then they would have to stop and 'check out' at the guard shack upon exiting. Disney would probably make some extra money on it. It also might cut down on pool usage by non-guests!
There are times of the year, actually starting now, that you can't park at the Epcot resorts unless you are staying there! During Food and Wine weekends, no one is allowed into the parking lots unless you are staying there. So, be advised.