You could certainly 'afford' most players, but could you 'buy' them? Most top players are going to want CL football and the chance of a domestic title. Not going to happen with Spurs in the foreseeable future, but as I said, you could bring in a few very good players for that sort of money. The problem is, how valuable (cash aside) is Bale to the team?
All true - but Bale also wants Champions League football now. He's put in time at Spurs and is at the peak of his powers. Liverpool are dealing with a somewhat similar situation with Suarez. If he can't be convinced to stay, he must go.
I agree about his role at Madrid conflicting with Ronaldo's (though Crsipy could go back to United...unlikely, of course, but possible). We'll just have to wait and see.
I think Spurs can afford to sell him. He might be technically irreplaceable but Spurs don't need a 1:1 replacement for Bale. In fact, two 25 million pound players bought after selling Bale might be even better than one 70 million pound player in terms of meeting their stated goals.