valet parking falls into the same category as "free breakfast". as it is not a tangible item being handed to you, when the FD takes off the charge for 2nd night, they don't take away the bennies...for a variety of reasons. (don't check the rate code, don't even know you had it, don't know the rules, don't know how to add it back onto the bill, etc)

So your chances of receiving that type of benefit goes way up....thehuncamunca has the right idea...better for it to be a nice surprise (rather than) expecting it.