The likelihood is his body will breakdown at some point and he'll be joining Kane on the treatment table, however, Bale is a decent punt for Spurs at 12M a year. If he helps secure CL qualification then it pays for itself without the long term cost applications if his body breaks down. If Bale's going to get his passion back it's more likely to be at Spurs before anywhere else, so they are well placed to get the best from him. Spurs also need someone who has actually won trophies in their squad. Nobody has won fuck all. The marketing also writes itself. It will drive some revenue. I can see good reasons for Mourinho and Levy chasing him.
They will have Bale, Bergwin, Kane, Ali, Son, and Moura. That's an impressive arsenal to have. They just need to pray they actually stay fit. I wouldn't be surprised to see Bale at striker on occasion.