When you say that there is only so much you can do with Photoshop, do you mean that you have limitations in terms of skill or the software's capabilities?
I either case, I think there are resources here that can minimize those limitations. I own Campaign Cartographer 3, which is roughly similar in capabilities to FM8, but I haven't really used it in a couple of years because I find that Photoshop can do everything it can do and more.
That isn't to say that there is not a great deal of utility in more focused software, but perhaps you should ask for some guidance to work with what you have before you spend money on more software. After all, if you find that Photoshop is, after all, suitable for your needs, you can spend that money on a Wacom tablet instead!
Anyway, ask your questions, and you'll likely find plenty of people eager to answer!