Hey Red,
I think you'll find that some folks that are in the business of rebuilding these machines back to spec aren't concerned about absolute playback performance beyond what the original manufacturers envisioned. Rather, they're efforts are focused on bringing the machines back to original specs and as reliable as is practical at a price point.
That said, I can say from my own tweaking on the RS15xx series machines that the friction caused by the elements in the tape path have an audible effect on the sound. It would seem that the elements before the playback head have a larger effect than those after. I think that the "Isoloop" system employed by Technics complicates matters and I doubt that it's quite as difficult a "balancing act" to get all the elements to work in harmony on other machines.
The reversing roller is one of these elements and that is where the counter gets it's rotational energy to operate. As Doc said, tape counters aren't created equal and unfortunately, the Technics counter looks to be about the same as one you might find on a cheap cassette machine. What's more, there are two belts between the reversing roller and the counter. All these moving parts lead to erratic mechanical loads on the roller which will either lead to slipping between the tape and the roller or even worse, variations in tape speed (not likely but possible).
These things are certainly in the realm of "finer points" and I'm sure that the difference in sound would be difficult to hear on less resolving playback systems or tapes. It certainly wouldn't have been high on my list of things to do to improve the sound, but I did get the screeching counter every once in a while so the decision was an easy one for me.
One interesting thing to note is that, while at MiCom, Dale Manquen did a great deal of work on the reversing roller on the 3M Isoloop machines in attempts to lower mass and balancing the mechanical load.