I can't comment on the Economy/Self Park lots, but I used the Valet lot 26 times last year and earned a total of 13,500 AP miles through the various bonuses offered during the year. Plus I asked for and received complimentary parking twice for 1 week vacations (and they detailed my car for free the last time)! Now that's a loyalty program!
At the Valet lot, you can use kiosk check in, and ENSURE that your Aeroplan number is recorded. It always prints at the top of the receipt. I think only once my miles didn't post automatically. I have a contact name at Park N Fly, and I just sent her a copy of my receipt and my miles were credited a few days later. (PM me if you would like her e-mail address.)
With the current promos I can earn 250 base miles + 255 bonus miles + 200 bonus miles for SEs** = 725 miles/park. That's not bad considering most of my parks are just 2 days at a time.
**SEs get 1000 bonus miles after every 5th stay. Not sure about the other tier bonuses.