Something like the hats in TF2 or the way you bling out your guns in Army of Two would be a great money sink and could also be awarded for getting certain protags. Let's say I get the 2500 kill protag with my gunner's minigun, give me a golden one or something so people can look at you and know how much you pwn. It doesn't change gameplay, it gives us something to buy with all our money, and it's not a lot more than a re-texture, so it's cheap to do. And I'm sure a lot of people would like something like this.
I would LOVE different faces and armor. I dont really like my tank being a bald bearded guy, and hey am i the only one who wants a male ninja? It would be cool if there were different armor looks for the assualt and tank. I want customization FIRST, maps are fine as is. As soon as you add maps you get the people who dont have them and then the community gets split and then things get ugly. Im all for new modes tho.