Yeah definitely as a mystery guest you look at things totally different. I've been to several receptions and hotels as well, there were probably people around me acting up just to test the hotel quality, chatting about breaksfast and so on LOL. Interesting stuff to think about, when you've only been a real guest like me for instance, totally different world.
If you're ever in the queue to check into a hotel or to be seated in a restaurant, pretend to take a call on your mobile and casually say something along the lines of " I'll have to ring you back later, just about to do this mystery visit", then throughout your meal have your phone on the table and keep checking the time on it, as they're bringing different courses out.
You'll get great service