Most satisfying system change in 2017?

asp307,
The Chord Dave had the most impact on my system, but it was only one of several changes and they occurred at different times. I changed from Wireworld Platinum XLRs to Audioquest Fire XLRs, from Wireworld  Silver Eclipse 7 speaker cables to Clarus Crimson speaker cables, and most recently changed the standard spikes on my speakers to IsoAcoustics GAIA Is. 
 

Made a lot of changes this year...
Misc:
Installed 51 feet with ceramic balls in them 
Installed 5 Oyaide Tunami Power cords 

Digital:
Replaced an AQ cinnamon digital cable for VH Audio silver 
Replaced a Parasound Zdac for Audio Alchemy's latest
Replaced a Pioneer stable platter with a Cambridge transport

Analog:
Replaced a cardas phono cable with a furutech
Switched out a Denon DLs1 cartridge for a Clearaudio concept MC
Installed a VPI Analog Drive System

Removed all vacuum tubes from my system:
Replaced a Sonic Frontiers Phono amp with Audio Alchemy's latest
Replaced a 6550 SET Jeff Korneff power amp with Valvet mono blocks
Replaced a melos preamp with the Audio Alchemy preamp/dac 

All of the above changes improved the system dramatically with the single largest improvement being the SE solid state Valvet mono blocks. These are sweet amps!

@asp307 

My upgrades were all spaced out, just different things as I could afford or find them. But evaluating each change at a time was a step in the right direction for my tastes.

Nordost Heimdal xlr and silver shadow digital( aes and bnc)
Very open and detailed sound, not lean as some have described but every system will give different results

I moved part way across the country earlier this year, few changes to the basic system components, but:
1. room- longer, deeper room, with slightly higher ceilings;
2. new power subsystem based on a 10kVa Controlled Power isolation transformer
3. I installed a big Minus K under the turntable- a heavy Kuzma XL with HRS platform to isolate the table
4. I added new subwoofers- a matched pair of 15" Rythmik sealed boxes with a small DSP controller.
I did not do this incrementally, so the changes in the aggregate were significant though for about a month, waiting for the Controlled Power unit to arrive and get installed, I played the system without it-- the power here, even without the isolation transformer is better than it was in the New York metro area, probably due to newer infrastructure. Density is actually higher where I am now, in central Austin, compared to the Lower Hudson Valley of New York, (i.e., not in Manhattan).
In the aggregate, the system is quieter, has more dynamics and plays louder (without sounding loud). Part of that is the room, which is probably better, sonically, than my last room.

@asp307

Check your inbox.

See here too:
https://forum.audiogon.com/discussions/no-frills-balanced-ss-integrated-amp

Those additions to the system were done one by one over the course of the year and with several months in between each. Wasn’t planned that way...just how it worked out.  We don’t have a plan.