I definitely think Kenny has plenty more to offer us, like most have already said, probably more so as an impact sub now.
But I was thinking that when his pace has well and truly gone, what do people think about moving him back a bit deeper in the midfield? He's got the composure, technical ability and know-how to still contribute a lot. I can't think of too many examples, but it's not unheard of for a more technically able striker to convert to a sort of deep-lying play-maker - I can recall Dwight Yorke and Nwanko Kanu doing something similar for their countries, and more recently you think of Wayne Rooney etc. Lee McCulloch even went down a similar route.
I'm not suggesting this just the now because as it's already been said, he still looks quite nippy when coming on in games, but just a thought that he could still be useful in other ways even when his goal threat has dried up.