If you do decide to get the DLC please note:
There's a bundle up for FFXIII-2 that covers everything that isn't delisted except for two weapons and a costume for Serah (Azreal Bow, Seraphic Bow, and Style and Steel outfit). $18.99 combined for all.
There are bundles for Lightning Returns as well but it's a little less user friendly. To get everything for it you'll need to buy the FF Legends Pack, Samurai Collection, Premium Collection, Yuna FFX, and Tomb Raider. Combined total of $38.00. Plus an extra $3.99 if you want the Japanese voice optional pack.
Honestly of the two I prefer the DLC in FFXIII-2 as the colosseum fights are quite difficult and pretty damn fun.
Also if you're coming from the PC version Aerith's schemata is available as dlc in the 360 version of Lightning Returns. This was removed for some reason in the PC release though I know there was some attempts to mod it back in.
Nice research and yes the colosseum fights are fun.
Are the N7 costumes still available?