They drop OHT mats and Chrono Pages.And yes, it is worth farming since Aga increase the drop rates of card bosses.
Yeah, I have a lot of them...but I just collect them. Nothing happens. =/ Just lots of stuff in my inventory....I have all of each kind i think. What do you do with them? Google tells me to quit trolling...lol jk, but yeah I really don't know how to umm....i guess Activate them? how does that work?