This is exactly how you're meant to take disadvatages, although yes they do give you back some cp - you should not be taking them just so you can make your PC do what you want at a basic level, that is what your starting character points are for. If you're finding its not enough, then its time to reassess what genre you're playing (the GM might want a very 'mundane' and gritty game, where you don't come with three years military training yet - you're just a farmer who decided to go to war with a heavy bit of wood as a weapon), or ask them how come they're skimping on the cp.I took Disadvantages out of habit by then but not because I needed the points. It was enough to take Gentleman's Code of Honor and such and be all virtue and goody-two shoes like a superhero is supposed to be.
This seems to be reflected in other peoples comments of "never improving", which again I don't understand as a reflection of the system (with its many possible rules) as its a reflection of your GM. The training rules may take forever to get any progress on a skill - but those are optional and not the only way to improve. Your GM should be handing out CP after every session (or every few sessions, depending) and this value should reflect successfulness of your missions/quests/etc but also be enough to fuel the expected rate of improvement (which for a fantasy game tends to be quite quick).With 100 Points GURPS Fantasy, you don't get them now and never get them.
There are many magic systems in GURPS, although I will agree that the 'main' one sucks for being a blaster. It just isn't intended to be a source of 'dps' and its a common pitfall for new players (especially ones with experience in MMOs these days). The best way to cope with this is using one of the other more flexible magic systems which allow more free-form spell casting, or better yet pre-build (by the GM) innate attacks for each of the various types of damage spells (as that advantage specially was designed to be a source of 'dps').Not even magic. You have to "waste" points on Seek spells that do diddly squat. Damage spells are only one die. To get more than one die of damage if you have to spend rounds doing nothing to build it up. I remember once casting Fireball. I spent three rounds doing nothing to get 3d6 damage. The monster was dead by then.
Of cause all of this does require some GM knowledge of the system and its possible rules, although I dare say it shouldn't be too hard to notice when your players keep complaining they don't have enough cp to make a basic fighter or to improve at a rate they're happy with - and the solution to that is a very easy one (hand out more cp!).
That said, I'll once again suggest Dungeon Fantasy (which starts with 250cp per character, which has some disadvantages already rolled into the templates) although the Wizard template is not a 'blaster' still (get the psionics book for that, the Mentalist in there is a very good blaster - so long as you don't mind saying hey to lovecraftian horrors from time to time). It does however come with rules for how much cp to hand out each session, and has loads of upgrade options which mimic 'levelling' except without need to wait for yourself to 'ding'.