Hi grandformage and welcome to the forum!
I would repectfully disagree that ARC is "ovet the top" (if that is indeed what you meant by OTT).
Without reliably lap counting in the very least most slot car racing sessions descend quickly into arguments about who is first, what is second etc.
While I agree there are other means of lap counting I think ARC does a wonderful job particularly to newer enthusaists.
A "Brillo" or steel wook pad is actually one of the worst things you can use to clean track I am afraid to tell you.
Newer track does have a protective coating on it that is destroyed by such strong abrasions. Older, regular steel track (i.e. yours) did not have this so it is less of a problem.
What is however a really big issue is the steel wool gives off tins, microscopic steel filaments that get pulled into the slot cars' motors and will cause short circuits and failures. It can even lead to cars' motors burning up.
Run the strongest magnet you can find along the track to pick up thise filaments.
Then use a strong vacuum cleaner on all the track you cleaned (be careful because the same filaments can damage the vacuum cleaner) or if you are really worried use compressed air first and than vacuuming second. Wear a protective mask as these filaments can get breathed in and damage your lungs.
Wash the track with high pressure water (not car wash high pressure but from a hose[pipe]) and dry it off by hand followed by using a hair dryer. Then run the magnet and vacuum cleaner again. (Tedious I know but that steel is very hard to remove).
There is a good section on track cleaning on the site. Our train friends at Hornby also have a track cleaning rubber/eraser that is good at removing rust without damaging the track or creating steel dust.
Even after all of this you will likely find the track not condusting electricity well.
There are several options such as using conductive copper tape to rechroming or soldering wires underneath.
Personally I got rid of all my "Classic" track except for sections that are no longer made in the new Sport" version, such as the Goodwood chicane.
Googling suggests the controller that came with could be better?
Controllers are a fairly basic electric device but essential to good racing. I am nut sure which version of controller came with the set you mentioned but at the end of the day any controller and be made to work with any analog track with some splicing and soldering.
What works best depends on the cars, the length and style of track and of course budget.
So since I want more track, and the set I used to have from maybe 1980 was ace for years of use, I could buy one of those round upright blue transformers plus the track from way back then?
Transformers (mostly) just convert AC power to DC power to a specific output in amps and volts. Ideally you have one transformer per lane to avoid power surges when a car leaves the track and bot of those should be identical.
How do I link old 70's/80's track to the X4 track to other brands and is new Scalextric track different again?
I can't comment on other brands but you can use teh C8222 converter piece to connect your "classic" track to the new Sport track.
The new Sport track is smoother i.e. less gripper.
What track length will one controller run, can two be used on the same two lane as a booster?
I don't completely understand this statement but you need 1 controller for each lane and ideally 1 power supply for each lane though on smaller tracks (less than 10 meters) one power supply should suffice.
Suggestions on why my carefully stored track is almost useless, even on new out of the box cars?
Rust does not conduct electricity I am afraid. Particularly in the 80's things were made to lesser standards.
Is older track grippier?
In general yes, but there are differences as the track was made in the UK, France and Spain all to slightly different roughness standards.