Very interesting thread. Value is so subjective, especially in this "sport" we've all chosen to indulge in. And as stated, there are others that may be similar (cars, watches, homes, hell...friends and significant others if you really want to go there).
I love my two sets of $15-20K 845 SET monos and 300B PSET monos. I also have a pre-amp in that price range. I now wouldn't consider living in my audio world without some system at that level...it has absolutely been worth that investment for me, certainly compared to stuff costing half of those prices (which were no slouches).
Would going up 50% in price, or doubling it, or more, make a valued difference? I, for one, would love to hear $40-50K amps and pre-amps and speakers in a well-matched system in my home, and see how much more emotion they might deliver. Of course it's incremental with diminishing marginal returns. At some point you will determine it's not worth it, like in everything. At some point there will reach a real limit, and you may even go backwards in actual performance. I don't know if I would justify going to that level, but I'd sure like to know what's possible.
I waited 22 years to buy a Porsche from the first time I went to look at one and considered buying it until the day I drove one home. I don't regret finally doing it one second any day of the week. I wish I hadn't waited so long. Worth it? That question can only be answered by you, obviously. Waiting that long also let me go big, which I did. Also no regrets there.
I do like the OP's question, although it does appear that the audience to answer is small as others have stated.