It's attention, not money, we should budget

The golden ratio for equipment $$$ allocation is as fallible as the golden ratio in room measurements.  IMHO.  I would agree with you that the biggest return on investment will be Speakers, Preamp, Amp and acoustic treatment.  

Interesting point. My budget has always been nearly non-existent, so bargains and DIY options (time) have been a requirement in assembling my system. In that regard I’d have to agree whole heartedly because time invested can pay off big.

If my income were much higher than it is now, I’d likely have taken a different path, but I’ll never know! ..... there are downsides there as well.

@erik_squires 100% agree spending time/attention and experimenting with an open mind can pay huge dividends.  It has for me. It seems to me many give up on a component/speaker prior to finding their true maximum performance and assuming a more expensive  purchase will be the solution. Often times leading to a  string of purchases feeding the used market.  In my case, I bought a used $9000 highly resarched/regarded amp to replace  a $3000 amp that had several easy tweaks.  The hugely disappointing new amp had inferior SQ and resold. However, other less expensive component changes have payed off after research.   Another example is when I restarted this hobby 3 years ago I bought a pair of speakers for $1400 shipped thinking I  could grow into them and then replace as they reach their max. They have shocked me with what they can do..I still own these speakers and I still hear SQ  improvement's out of them. (Tubes, fuses, cables, components, power…) In fact, I am hesitant to spend a lot more money to upgrade them and get inferior SQ and deal with the difficulty reselling large heavy speakers.  Granted this is just me, my ears and pretty modest system.