I beat it a couple weeks ago and am still finishing out the optional dungeons and after game sidequests. All I need now to get a platinum trophy is to get to level 10 fishing and beat the giant turtle (I'm worried the fishing part is actually going to be more of a pain than the turtle though).
I would have probably stopped playing since I was at level 67 and didn't want to grind it out to get to 99 in order to handle the after game sidequests but I found a exploit online that got me from level 67 to 99 in less than an hour. Here is how to do it. First you'll need as many Rare Coins and Debased Coins / Silver / Banknotes as you can get. Roughly 16 to 24 Rare coins should be enough to get you from the 60's to 99. Start crafting magic with 8 rare coins and 1 fire (do not load all the way up to 99, just 1). This gives you 5 expircasts at level 96 strength. Next you'll want to equip any moogle charms you have (if you don't its not a huge deal but it will help). Next you want to go to Wiz Chocobos and eat the triple decker sandwich (once you eat it once you can just have ignis cook it). It will give you a 50% exp boost. Equip the nixperince band.
Once you have all that ready go to hammerhead and go fight the Bandersnitch in the ditch north of the hammerhead gas station. It is level 38 and has a lot of health, this is good cause you want to kill it, but kill it slowly using as many of the expiracast fires as you can. Equip your team with crappy weapons (again you don't want them to do a lot of damage) and start using as many of the expiracast fires as you can, you might be able to get off 4-5 before it dies. This will net you 100 to 300k exp. Leave the area a little, save, reload what you just saved and fight the bandersnitch again. Repeat this whole process until you have 500 to 750k experience.
Once you have your 500 to 750k exp (and always having the nixperince band on) go to altrissa. Once there remove the nixperince band and stay at the 3x exp hotel (there is only one hotel in town, its got two people at the counter to talk to the one to the left is a 1.5 exp stay, the one on the right is the 3x exp stay) this will cost 15k gil. Again have the nixperince band off at this point. You will think get 1.5 million exp and it should max out your level.
Notes: The Debased coins / banknotes / silver etc. also give exp boosts in magic crafting, if you run out of rare coins use them. Make sure you always use enough to get the exp level in the spell to 96. Rare coins are better cause you use less of them and the spell is weaker and it allows you to use more in the fight. You don't have to fight the bandersnitch, just anything with enough health that you can get several spells off.
