Which cable do you think is most important?

One problem with sound is that it is "in the eyes of the listener". One can change speakers, change cables, change the room and all, to some extent, change the sound that you hear. For the better or not is up to the listener and there is, and can not be, any standard.

Remember that unless you are listening to music played acoustically, you are listening to processed sound and you are adjusting the sound engineer's perception to your perception. It's a losing battle.....and unless you have a different sound system for each sound engineer, what sounds good for one may sound lousy for another mix.

Now if you tune your system for acoustic instruments, you may find that anything that's been processed sounds thin or too much bass or whatever. Also, keep in mind that very very few singers are recorded pure...they are almost always processed in some way.

If you accept the above, you will not spend a great deal of time and money looking for the "perfect" cable.

Some say that 60% of what you hear from your system is your ROOM so you should spend money on room treatment first...your get the biggest bang for the buck there!...

 
Once signal gets lost or corrupted, no amount of expensive cable will recover it. If you have to spend more in one place, spend on the run from source, starting with tonearm to phono section or CD to pre-.

Otherwise, don't spend disproportionately in one area, cable your system with a single vendor's lineup at a price point that accommodates the cables you need.
 

"My system is in my living room and those tweaks would not pass WAF."

Having invested many, many, many $1000's in cabling and less than $1000 in DIY acoustical treatment, my experience is that all make a big difference, but the acoustical treatment is the hand-down winner in improving your sound the most and for a pittance compared to good cabling.

Try the Cathedral Sound panels from The Cable Company. They are the size and shape of a laptop and are covered in an inconspicuous light silvery-grey fabric and can be spray painted to match your wall color. They go in the top corners of your room, one in each of the front corners facing forward and one in each of the rear corners. Total cost is less than $400 for two pairs.

While not effective below 80hz, they will work wonders to clean up the mid-bass and lower midrange and only have a small effect on the upper midrange and highs. The only way I know of to improve <80hz frequencies is to buy/build large acoustical panels (like I did) or Tube Traps and it sounds like your wife is not good with that.

As for cabling, first establish a "foundation" with your AC delivery by adding:

1) 20A dedicated lines from your breaker box to your equipment using 10 gauge Romex and separating digital and analog equipment between the lines. Cost should be around $500.
2) Audio grade receptacles. I prefer the Teslaplex ($95), but also like the Porter Port ($36 here on Agon), many swoon over the R1 ($145) also.
3) High quality power cords, starting with your source. Good cords start at <$100 (like the Pangea cords from Audio Advisor) and great cords cost $1000's. There is most definitely a difference. If you can't hear it in your system, something is wrong with your rig, your room, or your ears.

When upgrading cabling, initially have your existing cables "cable cooked" by someone who offers that service. Then move toward improving speaker cables, then IC's (starting with your source), in that order, cooking them as you go.

Hope this helps. Good luck.