I've been debating the Model 3 vs buying out the lease on my Model S, too. But the time is getting short to order a Model 3 and still get the full tax rebate, plus I am still ambivalent about the Model 3. It would probably be a "better deal," economically, and it has newer technology, but I would miss the gray leather upholstery in my S, the sunroof, the power liftgate, the instrument cluster in front of me, and the spaciousness that lets me carry huge volumes of "stuff," even if I only need it once in a while. I drove used cars my whole life before I got the S, so I think I could go back to being content with having something that was not the latest technology and latest style. My car has been very reliable, I know its history, and the buyout price is more or less in line with similar CPO cars. (I know, I would not get the CPO warranty, so that is a factor in the price comparison.)
And if i keep procrastinating about making a decision, the decision will be made for me!