There's nothing "gold digger" sounding about saying, "Hey :) What kind of outfits turn you on?" unless you follow that up with "Sweet. Can you buy ALL OF THEM FOR ME? Thaaaaanks" ;)

It's hard to say what each individual is into. Some guys are super into slutty, others more elegant, like you said. You can find a balance between the two. Sort of an elegant outfit with something a little sluttier underneath. A garter and stockings under an elegant skirt and top can be sexy. Or some lacey/strappy underwear.

Sometimes it's not even so much about expanding styles and it's just about having more variety of the same type. If thongs are you preferred panty, just get more :) With different patterns on them. It'll keep his interest if all of a sudden you have a cute Elmo thong on :P

Most importantly, get things that you like. That you feel good, fun, and playful in. Daddies, in my experience, like playing with girls that a playful and fun. So if you are happy and in a playful mood, he likely will be too. Though YMMV :)