Your bike looks great as it is! I really like it. The only thing I might be tempted to do if it were mine is add a Brooks saddle, but that would most likely cost you more than double what you have into it already :|
Edit: And maybe a different tire on the back or both... Regardless, I'd take it out just as is
Yes, I think a cooler seat would be in order. I'm always on the lookout for bike parts. I'll see if I can dig something up.
What type tire would be cool for the back?