So... tempting. But I really want 1TB for vidya games. Currently installed games are already eating up 333GB, and that's after I recently uninstalled a bunch. I would like to re-install some more of my multiplayer games.
I usually build up a bunch of points and then see what area of the game is giving me the most trouble. When that happens, I'll put some points into improving that aspect.
That being said, since the Batmobile is used pretty often I'd put some points into it's offensive capabilities first. If you have good aim the increased damage to turrets is really good. The double dodge ability is good as well and I wish I would have gotten that one sooner. The hacking upgrade is also good in the second half of the game. Use it on the Cobra tanks.
At least the first grapple boost upgrade and batmobile eject upgrade is extremely handy for getting around the city quicker.
I always focus on combat offense first. Usually go for critical strikes, then lower combo score to activate special moves. Then the upgraded gadgets and takedowns are useful as well.