Well lucky me, I've a lovely yellow air cooler (three wheels and no suspension though). I don't think you need to worry about the "word spreading" about BIS's head gaskets and other realiability problems - they're famous for it, and I really do think it s because of a design problem (nothing is perfect). For example, the centrifugal oil filter has killed a lot of BIS's because its a pain to get to and a lot more like work than a throw-away one. Rot consigned most FSMs to the scrapyard after only a few years despite their indestructable engines. Its a good point that the aircooler's engine goes back to the 50s - when a car owner was expected to remove the cylinder head and decoke every year or two. These days, car owners don't even check the oil from one service to the next, let alone change it. This is certain death to an old engine so the 126 was way out of tune with the Western car market long before it ceased production, and was primarily being made as an Eastern Bloc budget car (with Eastern Bloc budget steel).
On prices, Fiat 500 has a very high price (£2k-£4k) because it is a 'design icon', like the Beetle - though there are plenty of both about. Most old cars don't reach anything like that so the 126 is doing really well being sold for more than a few hundred quid. The Fiat 600 (which I think is even better looking than the 500) is worth a lot less than a 500 despite its rarity in the UK (50 or so rhd?) - because it isn't as popular. The 600 Multipla is only worth the same as a 500 - it is almost unheard of in the UK these days and is arguably much more of a design landmark (the first MPV). My point being...? Well, I don't think there is any rational rhyme or reason to the value of old cars other than what people are prepared to pay for them, so maybe one day the 126 will be worth £10K? My hunch is that the early ones will become quite popular but the later ones will never be worth much, simply because of the trim - the later ones have lost that vinyl and metal frugal feel that pre-1970s cars had that makes them really distinct. One of the real differences between my 500 and 126 is the interior - the 500 ('69) feels like a 60s car, the 126 (1982) could easily be from anywhere between the mid70s to now, other than the noise and smell, of course! The trim, plastic bumpers, etc lack distinctiveness/character?. Still love it though, and very few cars are worth buying as an investment anyway, unless you are paying big money and are happy just to mothball it. And where's the fun in that?