Yea, 235 is actually a nice looking tire, especially in someone with some nub on it like the BFG's. It's not the stocker 215, but you still be happy with them.
Yes, regearing is your best fix so you can keep those 31s. If it was me I'd keep the 31s because I don't think the 235 is going to make a noticeable. I've driven my friend's 4 banger auto with 235 BFGs and they look great, but after having my 4.0L I couldn't ever buy a 4cyl. It's simply just a dog. I just don't think the 2 inches difference in tire size is really going to make that much a difference.