I did say tied to the captain in my last post, I did mean the crew, I guess I was just referring to them as one in the same. But yes I do think being able to level your crew in some way is a good idea. It will add value to your crew, because it is as Puchu says. Blowing up your crew just to evade being boarded or fighting to the last man isn't really the way thing's would have been done back then. There should be a reason to surrender and there just isn't one right now. Levelling them up doesn't have to be time/use based, it could be done as the captain is right now, through damage dealt. Then it's almost impossible to bot it or use a macro. Because you would have to actually be fighting. The only way I can think of being able to do it is stat padding and should be really easy to spot.
I'd like to even see some kind of XP debt if the crew XP is never gonna be an option. Could maybe scale with the amount of crew lost during a fight, means if you loose your crew enough times you could end up with a high enough rank to command a rowing boat . Just kidding, a bit extreme but just over exaggerating it to get a point across.