In Belzebub subforum have a lot of topics about this.
MF don't have any effect, but why not wear when gambling?
Some guys gambled at Hell, I suggest torment.
Difficulty and character lvl make more chance to come good items.
Gamble is more to find rings and ammys rares why good status, but you can try get specific items too, but is much more time/gold expending.
We need to update gamble like in Diablo 2 (every time you open the gamble) and make more good options to gamble, diablo 2 circlets/diadems are too good, rares here dont have too good affixes when not jewelry and staffs ;s