Hi, Porklet, and wlecome to the Grand and Munificent Hall of Cartographical Pursuits--otherwise known as, well, this web site. (Okay, nobody really calls it that big name, but I'm starting a grassroots campaign to make our site's name a bigger mouthful. Why not?)
My advice would be to pursue GIMP for two reasons: first, updates are always free, and the most recent version is surely beyond PS 4.0 in power. Secondly, when combined with your CAD knowledge, you could learn to do amazing touch-ups and finishing effects in GIMP that would fulfill your desire for "artistic" maps.
Now, if you already know how to use PS, this advice would change, perhaps--especially if you plan to someday purchase a newer version of the software. Familiarity may ease your pains in the future. But if you do not know PS or GIMP, then I'd say do the latter; spend time learning not the dead-end, but instead the free program--and GIMP is a great program (as you can see from searching our site for maps made using it!!)
Inkscape would be good too, but I'd say use your CAD skills for now and spend your time learnign to fix CAD work up in GIMP. Later, expand to Inkscape.
I hope my ramblings help! Welcome once again to our site!