Hmm... well, let's see...
Well, I saw above the comment about balance, since Glenn is a route dependant character.
I was thinking that perhaps he could become a non route dependant character, either by putting another character in that spot, or also make one of the Save Kid route characters also obtainable regardless of choice. If I remember right, the reason he doesn't join in the Save Kid path is that Serge and company head straight for HW, so he doesn't find someone to lend him a boat to head to Fort Dragonia. And he apparently gives up asking once they do return to AW or something like that.
I would think he can just keep asking for a boat and thus easily becomes a way for him to get recruited after returning from HW. It's not like say, Korcha getting mad at Serge for abandoning Kid, or spending too much time away from HW that Razzly gets eaten (because of this, if a Save Kid character can become non route dependant, my vote would be for Mel). His reason for being route dependant can be applied for both routes without changing much of it.
But well, that is only if he were to be a recruit in both routes.
I could go on, but for now I would like to see what's the opinion of the above first.