Are you playing the original release of D2:ED or DKS / D2:DC? There were changes to some of the skills as well as changes to stats and enchantments that effect mage builds.
Maxing Magic Missile is a good idea. You should also boost Destruction (and from what I've read Magic Blast handy), but you don't need to remove any points from Magic Missile to do so. If you are unlearning your skills anyway, I would probably take a look and see if there are other skills to reduce or drop entirely before taking points out of your primary attack spell.
Have you explored the battle tower (Mindread everyone) and used any skill books you may have had in your inventory? Have you explored outside on Sentinel Island? There are skill points to be had there, as well, depending on how you deal with the quest Turgoyn gave you earlier. There are 3 skill points to be had easily in the starting section of the fjords (1 from a mindread, the other 2 require something you may or may not have at the moment).
Are you having trouble with combat in general? If so, maybe boosting Destruction earlier would have helped.
Are you having trouble with single, strong opponents? If not, then not having Magic Blast isn't a mistake.
If you are playing DKS/D2:DC the hermit near the start of Sentinel Island has a necklace with a +2 Destruction bonus.
