I heard someone say "You're more than welcome," as I crossed a parking deck yesterday and it made me wonder why people say that and what it means. If Jane says "Thank you", and Bob says "You're welcome", Bob is being polite and assuring Jane that her gratitude is well received. I don't know if anyone outside of the United States tends to say "you're more than welcome" or even if you would hear it outside of the south, but the south is supposed to be known for its hospitality and manners and it wouldn't be surprising if the verbage originated there. Take "bless her heart", instance. I've never heard it outside of the south and depending on the context it can be used in one of two ways. It can be a sincere expression of someone's fondness for another person, like "Jane is a wonderful girl, bless her heart". It can also be used to soften a criticism and let the hearers know that the person uttering it does not consider themself mean for saying it. It lets you off the hook for saying unkind things. For example, "Jane is dumb as a brick, bless her heart", means that you feel sympathy for Jane's intellectual shortcomings and you'd appreciate it if no one would think you're a jerk for pointing them out. But now I'm on a different tangent.
I think "you're more than welcome" could mean a couple of different things. How about if Jane says "Thanks for explaining the evolution of the groundhog, Bob", and Bob says "You're more than welcome, Jane". What Bob might be saying is not only is it no problem to take the time to explain it, but he likes Jane and would possibly take 20 more hours to discuss anything she thought up.
When money is involved, it might take on a different meaning. If Jane says "Thanks for buying lunch, Bob", and he responds with "you're more than welcome" he might really be saying that he was pleased to buy lunch and he feels that they are good enough chums that there need be no thought of repayment between them and that it might even insult him and demean their friendship if she felt she needed to pay him back.
Now if Jane says "Thanks for the sex, Bob", "more than welcome" probably means that Bob is pleased enough with the sex that he would like to partake of it again at Jane's earliest opportunity.
"You're welcome" can be sincere or it can be perfunctory, but it seems that "you're more than welcome" must mean something, well...more. How about "you're more than welcome and you look good too!" but I don't know if that would catch on.