So I’ve been gambling a lot for this item type. GF Trav runs on my barb. Gone through about 20 million gold so far. Nothing yet that is either an upgrade or has trade value.
I notice that a lot of the blues have +3 to skills, or at least +3 to a certain class or tree. But I’ve never seen better than +2 on a rare. Can rares get +3?
Rare circlets/coronets/tiaras/diadems can’t get +3 to class skills, only +2.
One thing worth knowing is that rare Diadems can be indefinitely rerolled using the 6 perfect skull cube recipe without losing the quality of the mods. You can even roll a +2 class skill Diadem using the recipe with a level 8 character!
Another tip for gambling: Get a Gheed’s Fortune grand charm and make an Edge runeword bow for a total of up to a 30% gold discount! Buy 3 get the 4th almost free! 
Thanks that it useful information.
I have a good Gheeds, but didn’t know about the bow.