You can hyperspecialize, certainly, and it's something of a problem with mages, but in practice, a hyperspecialized character is easy to defeat. For example, one fighter might invest all of his points into Broadsword-40, but at that point, if he's ever without a broadsword, he's a wasted character, and he's also something of a one-trick pony. If my fighter instead invests points in strength, combat reflexes, Intimidation, Armoury (Blades), Connoisseur (Swords) and learns a few additional weapons (like, say, two-handed sword and flail) and master the Feint technique, then when we go toe-to-toe, I have quite a few options that I can use against you, like a switch of weapons to best defeat yours, the ability to bypass your defenses with clever tricks, better maintained blade and the ability to pick out that really good sword from that merchant's stand, and the strength to inflict superior damage and carry superior armor.
I've been running a 300-450 point samurai campaign, and while people could invest deeply, they never seem to. They're always branching out and broadening their abilities and exploring powers and other elements of the game.
You can run into some abuses, particularly with the disadvanteges: If I take -50 points in an enemy and you never bring him into the game, that's free points, and in previous editions there was definitely some "point crock" as GURPSers would call potential system abuses, but GURPS is in its 4th edition and it's pretty tight.
A bigger problem than seeing players break the game by becoming "too good" at something is that they'll forget something that's very important, or not realize that a skill might come up in a game. The classic example of the former is "Swimming," and a good example of the latter might be "Poetry," which actually comes up a lot, specifically, in the game I'm running. Templates can help overcome this by reminding players what they should take, which is one reason I recommend using them on your first few GURPS outings.
Well I might check it out at one point, if nothing else to see how it all works and what are the options. Might improve my d20 game in the end
