Went to Allentown last year and had a fantastic time. There are tons of pins for sale. Most people post their phone number on their machine, and have an asking price. It was fun to play hundreds of different pinball machines. Hit the newer machines first (get there as soon as it opens, of course), and reserve your time to relive the olden days in the afternoon when the newer machines have longer lines.
Some machines are in good shape, some machines are in really bad shape. Just depends.
Wish I could make it this year but too many other commitments. Have a fun time.