I have my own list of simple, but major "tweaks" to think about as well:
#1 Weakness timer - 5 minutes is entirely too long in 2013. FF14's is 1 minute. I think 2 minutes is reasonable for FF11.
#2 Allow the warp spell to be used by all jobs. Toss in a repetration spell too. Have it cost gil, bayld, conquest points, imperial standing, allied notes, moblin marbles, cruor, meeble marks, delve whatevers.
#3 Double the base skillup rate across the board.

That's really my short list of simple but major suggestions Really, the emphasis on new content in FFXI is all post-level 99 stuff, with so much gear to acquire, why not make the journey a little less frustrating to get there?