That is a cracking set. Well worth getting that than blowing a wedge on something new with only a few meters of track IMHO. If the motors in the cars are a bit tired they can be swapped out for about a fiver each. Both the Scalextric and SCX ones are readily available on Ebay. Tyres can be changed too as they harden with age.
I buy my braid in metre length rolls as it works out a lot cheaper than buying individual cut pieces. Also, wiping down old track with Muc Off brings it up a treat.
If you buy a bundle of old stuff may I suggest that you get a new Scalextric Sport powerbase, 2 transformers – one for each lane, new throttles (get a few as they are cheap – a couple of quid – and because they are so cheap you can end up with one throttle that is faster than the other, also you’ll have a spare for the inevitable failure), a digital lap timer and the connection pieces between new (Sport) and old (Classic) track. Ebay is your friend, none of the above costs too much and you should be able to build up an old set with a load of track for the price of a new one with hardly any.
Cars on the other hand can get a bit silly, but there are plenty of deals if you shop around. SCX work perfectly on Scalextric Classic track. Carrera are OK, but you have to faff about trimming down the guides. AutoArt look like a bargain but are rubbish.