Hey I wasn't upset by the 'ancient' comment!
Our cars in NZ tend to last a lot longer anyway because of not having salt on the road etc.
New cars are nice, when you can afford them. The 156JTD sounds lovely! I think in the Uno forum, most of us probably can't afford new (or new-ish) cars. And, those that can, decide instead to spend the money on amazing wheels and intercoolers etc.
Turbo seats - early Mk1 Turbo black-with-red-logo seats anyway - are rubbish as far as the covering durability goes. The later grey Turbo seats are excellent. However the actual foam and shape of the early ones is great - you would notice how roly-poly the standard seats would be in comparison.
The improvements. Three spring to mind. First, the vacuum advance unit on the distributor is really prone to having a split. Follow the pipe up to the carburettor, pull it off, clean the end, and suck on it (yes, really!) It shouldn't be possible to draw air through the pipe and you should feel something moving inside the distributor. If all you get is a gurgling noise then you need to splash out on a new vacuum advance capsule - it will make a really noticeable difference to the ease of starting, idling, etc.
Related to the above air leak, the FIRE carburettor is really sensitive to air leaks because it runs so lean. So, make sure the vacuum advance pipe is free of splits/cracks by flexing it along its length and looking closely. But also consider enlarging the idle jet in the carburettor. There is just one nut to undo to remove the air filter housing (and a clip under the front of the housing, to the cambox). The idle jet has a brass slot-headed top, the smaller of the two you will see. Unscrew it and you will find a small jet pushed into the bottom of the approx. 1" tube. I have had great success drilling this out to 0.55mm (standard is 0.47mm) - you will find then that the mixture screw on the carburettor will actually have an effect when you adjust it. Engine idling will probably be smoother straight away without any adjustment.
Third improvement: new thermostat. Usually the old thermostat become stuck-open, and the engine warms up to maybe 70 degrees in about ten-twenty miles or more. With a new thermostat, the engine warms to 90 degrees (centre of the gauge) within five miles. Oh that's right, you might not have a gauge (the 45 in NZ only had a light, but I think in the UK you did get gauges). Fitting the new thermostat is very easy as these things go (when I changed a thermostat on my 164 it was a week-long job involving re-sealing cylinder head coolant hoses and the drilling-out of a sheared-off, irreplaceable-sized bolt...)
Fourth, fifth, sixth etc. improvements: time the engine with a timing light (I use the hole on the gearbox bellhousing) by adjusting the distributor. Five degrees BTDC is good (vacuum advance disconnected and plugged). If it is right at the end of its adjustment, pop off the cambelt cover and just check that the cam pulley lines up with a notch at about 43 minutes to the hour with the crank at TDC - someone may have mistakenly assumed it to be horizontal.
Lubricate the clutch cable with some general-purpose grease, by popping off a clip on the clutch pedal pin, taking off the cable, and greasing the pin. Also grease the semi-circular block on the clutch release arm. You may like to grease the cable itself, but this is probably not necessary; just the end fittings.
Check that the choke linkage is adjusted correctly with an appropriate amount of fast-idle, so that the engine idles ~1500RPM with the choke at the first (non-enrichment) notch.
That's really about it - if the alternator belt squeaks or looks glazed, replace it (cheap as chips), and of course change the oil if not already done so.
Incidentally, the FIRE engine is 'non-interference', which means that if the cambelt breaks, you won't have any bent valves to worry about. You won't be driving home either, but at least it will be a cheap fix! Actually, changing the cambelt is very easy so if it looks aged/cracked you would probably want to.
The Uno is an easy car to do jobs on yourself, and as such it makes great low-cost 'backup' transport. I think you'll find it surprisingly reliable. Even if every single service item is shot, it's still good value in my mind because you know what work has been done. Unlike if you take a modern car in for a service...
Hope it goes well for you!
-Alex