I prefer using file guides over multi-angle tools when tuning my race skis, although I use the multi-angle tools on my recreational skis. Some multi-angle tools can vary greatly in accuracy from use to use, since the edge angle is set by a small screw. Others use a series of wedges, which I find to be much more consistent. Whatever you use, let the file do the work- don't press down.
As has been mentioned, use relatively fine files to maintain your edges. If you do a quick sharpening every couple of ski days, you'll be able to use less-aggressive files. Detune the tails with a gummi stone.
Skip the annual base-grind unless you get a lot of base damage. Have the shop set up you side and base edges once, and then avoid the grinder after that unless absolutely necessary.
Make friends with a good ski tech and get them to teach you how to maintain your skis. You can read a million books on ski tuning, but you can learn a lot more by seeing someone do it firsthand. REI and other sports retailers often have clinics to show you the basics. The Swix alpine ski prep guide is also a good reference.
Keep your tool kit simple, but buy good quality tools. The Swix mid-line wax iron has a double-thick base and holds heat better than the economy iron. I use primarily bronze and nylon brushes for basic waxing. You can't brush your bases too much. Unless you're racing, stick to hydrocarbon waxes. The more you wax and brush your skis, the more wax the bases will retain.
It's really easy to go all gearhead when it comes to tuning, but a few basic skills are all that is required to make fast skis. I stopped by to talk with the tech that tunes for the US Ski Team as he was prepping skis for their camp in Chile. I watched as he prepped some Super G skis- working carefully and double-checking everything. No fancy machines, no really high-tech gizmos, just patiently working with basic tools to turn out a superior ski. Keep that in mind when you're looking through catalogs.