Well, the $20 "tip" has been discussed on numerous Vegas message boards for ages and the general consensus seems to be that it is more effective at the cheaper properties, i.e. downtown or the cheaper strip properties such as Tropicana, Flamingo..etc..

The room prices for suites/great view/..etc..can be quite substantial at the higher end properties such as MB. Therefore the hotel frowns upon guests with a special offer/discount reservation being moved to a 300/400/500$ a night room because they slipped the clerk a $20.

That said, it always depends on the actual clerk at check-in but your chances of this working are pretty slim...

The good news is that the MB is a great hotel and the normal rooms are perfectly adequate, i.e. very big, big bathrooms..etc. You will have a great time at this property, regardless of room. The beach/pool area is fantastic, spend your time there, not in the room

Enjoy your trip !