My take on the matter??? I think Disney CM's are trained NOT to be bribed!!! I don't think you can "bribe" your way to a better room. There seems to be no consistent variable as to why some get an upgrade and some don't.....I think it depends on #1) the availability of rooms to upgrade to AND #2) the "whim" of the CM who is checking you in....
It's like calling CRO and talking w/ the CM's there....They can be night and day from each other! I called one morning and got one CM who had as much personality as a rock....He gave me little help at all in answering my questions (as a matter of fact, he gave me some incorrect information!) Then, I called the next morning and spoke with a wonderful CM who spent about 1/2 hour with me, giving me all sorts of pointers and tips to make our vacation perfect!
The point??? If the first CM I talked to also worked at the front desk at check in, I guarantee I could give him $1,000 and he wouldn't do anything for me.....On the other hand, the 2nd CM that I talked with, if she worked at a front desk, I imagine she would do everything possible to make my stay perfect and would never take a "tip"!
I think your best bet is to be chatty(in a nice way) at check in, expressing how special this trip is to you....especially if it's your anniversary, honeymoon, grandma's first time....
If you want to be bolder, maybe say something like, "I hope I booked the right kind of room.... I really wanted a XXX (water view or whatever upgrade you wanted), but didn't think we could afford it." Then, I would drop it! You've made the hint....if the CM is the type to pick up on it and do something about it, then they will if they can. If they don't get the hint, then all the money in the world won't change what they do for you!!!
And, the bottom line is, if you expect nothing, you won't be disappointed. If you then do get an upgrade, it will be a pleasant surprise.