Something in me feels that while this ability is fine at face value,
that it just shouldn´t work for non-arcane Wands / off Wizard-list spells.
(at first I thought off-Magus list, but they are presented as para-Wizards, and I was OK with that)
If they want to use UMD to activate a Divine Wand, fine, but their INT bonus shouldn´t really kick in there, given UMD is a CHA skill in the first place (even if maxing ranks in it via Headbands is more effective than just having 18 CHA). Especially given that Wand Wielder would be letting them use these Wands in combo with their SpelL Combat schtick and related abilities.