That wouldn't work cause with a good group you could easaly farm Ifrit and Garuda quickly meaning you have an easy time to cap the tomes.
They should make it so that you can't get more tomes if you cleared it more then 3 times each day, that would avoid the whole doing all day the same instance, in general i think the problem is that they only added 1 dungeon lvl 50 which everyone need to run to get their gear updated. I mean why couldn't they add like 3 dungeons where each dungeon drop different gear so everyone has to do the 3 dungeons. Add a daily dungeon with double tome bonus and everyone will do pretty much each dungeon daily, problems solved.