Probably if I had a steady stream of income I would.

Makes sense. Just because you have a high discount rate doesn't mean you have a high tolerance for risk; there's a fine line between wanting to redirect your future income toward the present and wanting to spend now at the cost of going bankrupt later

.>I really did mean (3), and I'm not ashamed of it.

Well, at least that clears up your motives -- they're pure. Sorry I doubted you. I thought maybe for a moment that you just liked showing off calculus, but I guess you were just trying to attack a really hard problem. This comment is sincere, not sarcastic.

But I'm not sure we should avoid a question just because it's hard to answer.

Avoid, no. Save for slightly later, yes. In my opinion, the much easier and nearly as useful problem of calculating medium-term net present value should have been solved first, and then once we all understand that and have begun to apply it to our everyday lives, then it's time to try to solve the much harder and only marginally more useful problem of calculating instantaneous net present value. But, you know, you're the one doing the work, and (not knowing you) I have no reason to distrust your estimate of your ability to solve a really hard problem. So, good luck!