I still don't understand the question. Is it how much we have spent on our current system(s), how much we would like to spend before diminishing returns (for me/us) set in, or how much is the least expensive musically enjoyable system we think we can assemble?
I think you are right!
The answers in this thread, however, suggest that most of them interpret the question in a way that it is the system they own... How could your personal vote in $$$ be wrong...

The used/new discussion makes things even more fuzzy. Looking just at my Bryston components (14B SST, 2x 6B SST, SP1.7, BP-25), they easily surpass the $30k in new list price, especially if you consider the higher prices overseas. On the other hand, I have paid a fraction of that amount buying the stuff used.
As most of the users that have replied here, I didn't wake up one morning and decided to spend a fortune on my audio/video setup. For me, it was more like starting small and improving the system(s) as funds and opportunity were given. Of course, technological advancements and new formats also trigger investments that often trigger other improvements.
On the other hand, I have heard small and relatively inexpensive systems, that have an incredible performance. As a stereo setup, I currently run a BP-25 Phono with a pair of Dynaudio Focus 110A active monitor speakers and a Logitech/Slim Devices transporter as a source. On the used market, you can get the components at around $4K and the performance is stunning. I also like my kitchen system with a B60-R, a pair of Dynaudio Audience 42, a Logitech Squeezebox 3, an ancient Kenwood DP-1000 CD-Player and a great sounding Kenwood KT-1100SD FM Tuner. If you are lucky, you could get the components used at slightly over $1K and the performance is at a level, where an audiophile doesn't have to hit the "emergency off" button, which is the case with so many low quality setups...

O.k., that's another 2 cents.
Cheers!
Markus