My two cents for what it's worth.
From what I've seen and read, there is a smaller return for the money on more expensive items meaning that the differences in really expensive stuff is realized by people with particular tastes and the equally expensive equipment to bring out the best in expensive items.
To answer the OP's question, it may well be that a $4,000 new speaker gives much more bang for the buck than a really expensive speaker with the OP's taste and the electronics on hand.
On the other hand, for those regularly bitten by the upgrade bug, buying beyond your current equipment's means could be the more economic route.
Personally, I stay within a certain price range though that price range seems to tilt up a bit each year. Perhaps, though, the answer is to just listen to the two hypothetical speakers and pick the best for you.