;^) Here's a trick that will help you to level anything up more quickly: To level anything up, you must collect the blue ABS crystals that monsters drop when they're defeated. Also, tougher monsters drop more ABS crystals. So, you want to travel to the latest dungeon that you've unlocked and level up there.
Here's the trick: you don't have to defeat the monster with the weapon/monster that you wish to level up. Instead, defeat him with your most powerful weapon so that it goes faster, then switch to the weapon/monster/ridepod that you wish to level up before collecting the crystals. All of the experience will go into the equipped weapon/moster form/ridepod.
Using this trick in the last few dungeons of the Zelmite Mines will yeild enough ABS to jump a level 1 monster badge to level 4 with just one monster, for example. By the time that dungeon is clear, the monster badge should be about level twenty-something, if I recall correctly.
:^/ Bear in mind also that the higher you go, the more ABS are needed for each increase. So even when you use this trick it will take a while to max them all out. It'll just take less time than it would otherwise....