Responses from ferrox

Tube vendors.
As for me, Vintage Tube Services. 
Need speaker advice
Audiokinesis seems workable for you. 
Sound quality impact - preamp vs power amp?
In my personal opinion, a preamp works like a music conductor. I have both Aesthetix Eclipse and Atma-sphere MP-1. Both are excellent preamp but have totally different presentation of the music. It's like listening to Bernstein or Karajan in compa... 
Do speaker wires matter
I have been changing my speakers cables, from Siltech, JPS Labs, Acoustic Zen, Gotham Audio and I now ended up with the vintage WE cables. It always makes different when we switched the cables. It's all about the taste and the matching of the whol... 
I would not comment about overrated, but for underrated, for sure is Audiokinesis speakers. The best bang for the money. As for the audio gears, Aesthetix and Atma-sphere are entitled for bigger acknowledgement.  
Point of higher priced streamer?
Coming from Auralic Aries femto to LDM Server. It's a huge jump. I even tested two different firmware of LDM intensively for a week to compare between the two. Apart from the server itself, the firmware also plays a big chunk of the audio journey.... 
Should I use long interconnects, or long speaker cables?
If your preamp had xlr output and your amp xlr input, use longer xlr interconnect. 
Most hyped turntable, tonearm, and cartridge?
Sota Sapphire V with proper setup and affordable arm / cart, will sound wonderful as well.  
Speaker Positioning
Start with laser distance measuring device and you can tweak it from there. 
Unbelievable 3-D imaging sound
Totally agree with you, when a system totally dialed in, it would give you the most thrilling enjoyment. It's a real pleasure to experience every mm move we make on our speakers and observe how the sound stage changes. :) 
Cartridge recommendations under $2500
Benz Micro Wood is also worth considering. 
High end stereo preamps? Worth it?
Bring in Aesthetix preamps at any level. It will reveal what music is. :) 
Which USB Re Clocker
My take is Ideon 3R Master Time. 
Dac upgrade
Try looking for Lampizator DAC..they're amazing.. 
Put your best powercord on the initial line..either CDP or Preamp for best result.