Is Ryzom one of those top-heavy games where players need to party with team members that are close to the same skill level? What I mean is, could a new player be useful in a group that is comprised of mostly old characters?

Most players have low lvls in one form of melee or magic or another..... Just because you master 2 handed melee does not mean that you can use Q250 skills with close combat.  Those lower skills need to be lvled up and new players can help.

Newer players can also help as healers.  My only caution is don't get stuck in a lot of plod teams, cuz they can get boring if that is all that you have done from the time you leave Silan.

Crafters are always needed, because you can not repair gear.  It must be replaced and the stuff you can buy from the NPC's is pretty horrid compaired to what players make.