I don't know if they exceed the 300 level cap. I assume so, but for the tradeskills, it wouldn't exactly benefit you. The advantage - while you are still leveling - is that you will be able to create items sooner. A base of 160 with a +5 bonus will let you attempt 165-skill items sooner.
Having 5 extra skill in a weapon, AFAIK, doesn't affect crit rates. It DOES affect hit rates though, so you would effectively be able to hit creatures one level higher. (I'm real fuzzy on how weapon skill actually works, but if I interpret correctly.)
And I won't say they don't matter at all to you. You're obviously being choosy over creating the supa character. To that extreme, they do matter, but again, to that extreme.