While it is doable, they very much enforce the Party bracelets. Party visitors start coming into the park at 4:00 and the regular day-visitors are asked to leave by 6:00 but they give you an extra hour to mingle around the stores or restaurants (Not the rides)...after that, they really do start checking the bracelets after 7:00, even to enter stores and restaurants.
Actually, I was there once and had them start checking bracelets around 6:45. There was no "extra hour" to hang around, the park doesn't close for regular guests until 7PM, at least on the night of my experience.
Cast members were
extremely aggressive (for Disney) about restricting movement. My wife had to practically force her way past a blockade of cast members to bring my then 2-year-old niece to the bathroom so that we
could leave. And again, this was well before the park closed to regular guests.
However, all this appears to happen only around closing time. We were there a couple of nights later, this time for MVMCP, with bracelets. The blockades of cast members were nowhere to be found, and any checking for bracelets that was going on was quite unobtrusive.
My advice would be to just go to MK on a non-party night. You're not really missing anything with the party, IMHO. The snacks weren't anything special - hot cocoa like you can make at home from powered mix, and sugar cookies that had been frozen and (mostly) defrosted after they were baked. The parade was nice, but I'm not a parade guy and could have taken or left it. Fireworks were also nice, but I prefer plain old Wishes, and you can view them from outside the park anyway if you're really that interested.
By no means would I let myself get caught inside the park within a half hour before closing again. I've never been subjected to such un-Disney-like treatment anywhere on Disney property.