Grimrock

Now my party is level 12/13 and because I'm a fan of concentration in character's skills, e.g. my Rogue has Daggers 33 an Dodge 24 and the one mage Ice 32 and Spellcraft 18. For me it looks like there is nothing really interesting skill to come.

Now I wonder whether it's a good idea to learn something new like Missle-Weapons or Air? My gut says no but what did the experts suggest? Are there enough to come to reach a useful level?

We stand in the Goromorg Temple (I) now.

The capstone abilities (level 50) for nearly all of the skills are pretty bad ass. If I were focussing entirely on making the most powerful party, I would try to get the weapon skills especially to level 50 (double attack speed). However, Grimrock is a fairly forgiving game - as long as you don't spread your skill points out equally across all your skills, I think you would have to work hard to make a 'broken' character.

Above all, I would say just have fun - if you want to play with some different weapons, don't worry about not being optimal and just enjoy it :p. I rarely min-max in RPGs as I like to play with different game elements and not restrict myself to only using 1 part of a game world / engine.