I don't tank, so I couldn't really say what would provide incentive for them to queue up for 50/60 dungeons. EXP only goes so far. You don't want to toss in rewards that are acquired elsewhere if it threatens to make it obsolete. Glamour incentive only lasts until it's obtained. Mats will attract crafters to queue, but not all of them will tank. Ventures, tomes, gil... all are things that most can take or leave.

Perhaps what's needed is something new? Perhaps random drops that can spawn S ranks or something? Maps that can be soloed so they don't have to level a gatherer or buy them from MB? Introduce new dyes and toss them in there? Just a few suggestions off of the top of my head.