I don't know if you finished the training and got what you are looking for, but here's an answer to all the questions I can imagine being asked about it:
*I'm just going to say spoilers are below, in case you're someone who doesn't want to know what you're unlocking ahead of time*
After completing all 25 basic training and all 25 advanced training levels (reaching bronze or above, as long as you complete it), you unlocked AI Enemy Battle.
The options you can select are:
Maps:
Map 1 (It looks like Cube or something, I dunno I hardly play online MP)
Map 2 (Pirate Fortress)
Map 3 (Another arena that looks like Cube)
Map 4 (Turbulent Jungle)
Map 5 (Don't know the name of this map, it takes place in Central City)
Game Types:
Elimination
Team Elimination
Post Grab
Counter Grab
Akrid Egg Battle
But those are the ONLY options you can select. You cannot select score limit, time limit, layouts, friendly fire, etc. You can ONLY choose one of 5 maps and ONLY one of 5 game modes.
You DO receive career points in the AI Enemy Battle, but not as much as if you would play online My personal opinion is that it's worth it if you don't find the training mode to be too hard or if you want multiplayer and can't play online, but if training is extremely difficult for you and you can play online anyway don't finish all the training just for the sake of a secret mode.
(Edited, I originally said that you got a very poor xp rate, because I played a match where I was in first place with 500 pt, but then I played some more games and was getting over 3,000xp)