Andy, face it, you can't predict if a player turns out to be a success or not.
You were happy about Tiago, he turned out to be shit. You didn't want Iaquinta, he turned out to be very usefull for us. Its hard to predict if a buy is a success or not. Time will tell, but at the moment, he is for free and this makes it a good thing for us. He could be usefull.
All of the other arguments (finished player, behind his prime) we can only judge, when we see him play for us again. Finish!