The "$20 trick" is an iffy subject. Sometimes it works, sometimes just asking for an upgrade will work (it all depends on how busy/full the hotel is expected to be...ask your valet, they'll know). If you walk into the hotel and it resembles a zoo - hope for any upgrade (hard to do if hotel is full of paying customers). I love doing the $20 trick...at worst we've still received a nicely furnished, high up, strip view room. At best, we've opened the doors to jacuzzi suites, 3 room suites, top floor amazing view rooms, etc,etc.
We have several hosts that have really taken care of us. This is where knowing a little something about your host helps (pick up the phone and chat with them for a few moments). I do not know of a host that is allowed to accept cash and many are on never ending diets, so we have found that gift cards work well. Our favorite hosts have "families". One hostess has teenagers, so gift cards for Blockbuster video make her happy (and her home quiet). Another host has 3 small dogs - Petsmart it is! Many of the hotels have coffee shops (ie: Starbucks) and gift cards from these make GREAT gifts, especially if you're not familiar with your host (plus these are easy to pick up while in Vegas). Put your gift card in a thank you card addressed to your host (in case your host is off duty, it can still be delivered to their office mail box).
Good luck, and have a STRIKING trip!
Tammy