Honestly you can get fairly professional looking results with a spray bomb. I'd suggest practicing on something else first, maybe a flat piece of scrap aluminum or something, to get the "touch." But I bet I could spray bomb a case and make it look like it was professionally done.
tips:
1) sand it smooth. Prep is key. If you are going for a smooth, glossy finish, use a sanding block on the flat bits. Probably 320 wet/dry paper used wet if you are using Krylon or touch up paint from the auto parts store. If you are using vinyl dye or model paint go smoother, probably 400-600 grit minimum. 1000 or 1500 may even be required with vinyl dye; I've never tried it. Keep it wet! If you start to see "pills" of material, you're not using enough water, and those pills will leave marks that may show through the paint.
2) Post-sanding but pre-spraying prep is also important. Wipe down with Windex and a microfiber towel, then use a tack rag or painter's tape to pick up any lint that may be left behind. Again, it'll show through.
3) Paint on a good dust free surface. Cardboard ain't it! Either rig something up to hang the part, or else if you are painting on a flat surface, set the part elevated on a coffee can or something so that dust isn't kicked up off the surface onto your part. If you paint with the part laying flat on cardboard, you're almost guaranteed to have that happen.
4) follow the directions for recoating on the spray can. A few light coats will give a better finish than one heavy one. The first few coats can just be "dust" coats, and let them flash before recoating. If you try to do too much too soon and there's any contaminants on the surface, you'll get fisheye big time. I'd recommend using a sandable automotive primer and then wet sanding again if you really want a good glossy finish, THEN use your color coat (only if you are using paint and not vinyl dye though.) Make sure that the primer is 100% dry before wet sanding (see "pills of material" above.)
5) If you really hork up, DOT 3/4 brake fluid will strip paint from most plastics without harming the plastic. (a tip from having built plastic models back in the day.)
6) If you've used paint, and want a super gloss, get some clear enamel or epoxy (if such is available) spray to finish it off. Either spray it while the color is still tacky but flashed or else let the color dry completely (at least a couple days, possibly a week,) and wet sand with 1000 grit before spraying the clear.
7) if you really want the ultimate in gloss and durability you will have to at least do the clearcoat with a spray gun using a two part paint with a hardener. I am not that hard core... I'll do that for a car but not a keyboard. Your opinion may differ. If you do do this might as well wait for the clear to dry completely (a month or so) then wax it. I like Nu-Finish, but YMMV.
Hope this helps...
