not sure on the fuel front for a 1-litre - going by the manual they seem to be a bit more resilient than the other engines and intended to run on leftover vodka when times got tough in the east european countries they were also sold in

certainly putting super in mine never made a jot of difference (no knock sensor for starters - it'd help if you were to e.g. manually advance the timing i guess).. 95RON is a good 4 steps above it's minimum rating.
similarly the "carb" - apart from the injector nozzle, that may need the odd one-shot of redex if you tend to run on cack fuel, this stays totally clean and doesn't need anything like the attention a mk2 one would. when i dismantled the engine, this part of it looked as good as the day it was fitted at the factory. benzine (petrol) used to be used as a dry-cleaning agent after all...
and also if it's a mk3 the ignition's all electronic - the only setup you can do on the timing is the basic advance that underlies all the trickery that the ECU does on top... probably doesn't have anything like the effect that altering the cam timing would, these days.
(that's what the sports ROM chip does - covers the twin avenues of sorting the fuel mixture and spark timing that playing with the dizzy and carb would have done in t'olden days)
But, the other stuff is all good - very much reccommended to have a clean air filter or even a custom (cleanable/reusable) K&N intake if you want to splash out a little (the golf mk3 conversion is well proven for the 1.0/1.3CL/GT, and quite cheap), i've felt the effect of a clogged one before (followed a few too many trucks and got it jammed with soot after 4k miles) and it's fair surprising the difference it makes!
Dodgy ignition leads can BADLY hurt your low end torque, not to mention damage the engine (basically, you get chronic misfires at wide throttle below about 3000-3500rpm). Particularly noticable in the wet. Same goes for anything else thats wrecked in that department (dizzy & rotor, plugs, etc).
Fuel filters are less than a quid a time, so if you've got the time and knowledge to change it, you may as well.
And naturally it doesnt pay to murder your block with sludgy, swarf-heavy, poorly circulating oil and a clogged filter. This can be no more than about a tenner each 5000 miles if you buy the stuff at GSF, and worth the very slight increase in outlay over doing it every 10k.
Other than that, make sure your exhaust is ok, no holes etc, (de-catting it was probably the best thing you could have done - it robs close on 5 horsepower!), keep your tyres up to pressure, and be ruthless in removing unneeded gear that you might be carrying.