It's very hard to argue against the usefulness of arcare. With 21 points in arcane you get essentially two instant spells, arcane missles and arcance explosion (also an aoe). You also get Evocation which is very nice, Prescence of Mind and improved Counterspell. These are all very helpful, some might say essential spells and improvements.
However, one can live without them. An all ice mage has some awesome survival and kiting skills, plus real damage. An all fire mage can kill incredibly fast with the best burst damage in the game.
I think Fly is right when he says that elemental mages are gimped, but they are still viable. I'm currently using a 44 fire and 7 frost build. It's more of a speciality build based on what I want to do with this toon. I think it works very well for PVP (think Warsong Gulch) and to help solo high level elites.
Lately I've been grinding Warsong Gulch. I think it's fun and different and though I'm sure I'll never get that high there's some possible rewards down the line. This build seems to work really well. My frost points are spent in Permafrost, which increases chill effects, and Improved Frost Nova which reduces my the cooldown by 4 seconds, both very helpful in PVP. Combine this with the burst power of the fire skills and I've done quite well. I'm almost always in the top 3 on the alliance side. This may be normal for mages with decent gear but I think the build helps.
I also like to solo elites in Tyr's Hand and Winterspring. The drops are great and so is the challenge. From what I understand pure frost mages are better at this because they can kite the dudes but this build, again, works well for me. Pyroblast as an opener (often with Combustion on top) is perfect for these mobs.
Anyway, I love the debates about builds, and God knows I've spent tons of gold trying out different ones. The BEST build is probably a 30/21, with your pick of 30 in fire or frost. I also would say there are few bad builds.
Good luck!
