Best bang for the buck

Well, I spent it on a person, rather than equipment. I bought a day and a half of Jim Smith coming to my Boston area house (from the Atlanta area where he resided). He is the author of "Roomplay" and "Get Better Sound," and he could be hired to come to your house, take measurements, listen, and listen some more. He had me change the direction that the speakers were firing, and spent a lot of time tweaking speaker placement and seat position. 

When he left, I had a much better sounding room than before he came. I'm still in the same room, though I have had a few different speakers since then. But his principles guided my set up thereafter. It cost about $2,000 back around 2010 or so. Better than a new set of cables, I think...

David

Most bang for the buck was a rug to counter the floor sound. However I've switched to e-stat and this is no longer needed. I don't have any other bang for the buck, everything is so expensive.

Hands down, room treatments, all stop.  I've got a fully treated room and finally got around to putting some Rockwool insulation in the crawl space under the floor and got a transformative SQ increase.  $250 well spent.  

@rick_n Have to agree- room treatment is a very high value proposition. When I moved I spent about $1000 on room treatment- incredible 

My speakers cost me close to $1000 in parts to build in 1989, and I've managed to build a system around them that I've loved for decades, and will very likely be with me for life.   Got my money's worth years ago.