I do not like my chicken tough, but I do not want it mushy either. I want some texture to it. I suppose one could always grind the older chickens and make chicken burgers if they wanted too. I have thought of doing that. I also saved the fat, we do not use lard anymore, from the last pig we butchered. I plan to make some chicken sausage and wieners with that in my smoker.
Actually if you want to eat older chicken and think it is tough, I would think marinating them in vinegar or tenderizing base would help. Also there are so many dishes you can make with chopped chunked chicken. Chow mien, hot dishes, casseroles for those of you not in Minnesota, soup of course, chicken salad, and so forth.
I think slow baked roasted chicken would be okay, Use salts or accent meat tenderizer on it.
I am just against slow cookers, I think we over use them and the meat in a slow cooker tastes "blaw" to me. IMHO
Another addition if you have to use the slow cooker, I suggest cream of mushroom soup, wild rice* a few onions and mushrooms.
* Minnesota style wild rice LOTS of rice, like a pound or so, not a little packet, like they passed off as a "wild rice casserole" in Florida when we lived there.