That's a nice idea for a tribute
I have two cars (owned for 21 & 13 years respectively) that I also never intend to get rid of.
I think the best form of future-proofing is to stop it rusting. Everything else can be replaced.
On these cars, that means the rear axle (although even a replacement isn't too big of a job). I
wire-brushed & painted mine, or you can get a garage to Waxoyl it.
Happily, these little FIATs have pretty good rust protection on the structure & bodywork, but some Pandas of similar age are showing signs of rust in the rear sills. I just pour some old engine oil into the cavity at every service (there are rubber bungs in the rear wheel arch & b-pillar), but again Waxoyl/Dinitrol or similar would be good.
A smartphone endoscopic camera is a good way of monitoring rust inside cavities.
I'm of the 'if it ain't broke don't fix it' school of thought, so I don't think there's much point removing functioning components, but fresh springs, shocks, front suspension arms, drop links and brakes are a good way to freshen up an old girl. Stainless exhaust?
New fluids are always a good idea, especially if transmission oil, coolant and brake fluid has never been changed.
Paint is one area that can show its age, so maybe a trip to a bodyshop, or some elbow grease with detailing products. Some sort of clearcoat will help preserve the paint.
Interiors are plentiful now, but might be hard to source in future, so a spare set of matching seats might be an option if you have space to store them. Maybe just the front seat bases, which take most of the wear.