I think that TAF Golds do actually make for an interesting pinball anomaly.
In many fields old/ rare = valuable. But I don"t think this applies in pinball unless you are talking seriously rare like Pinball Circus.
TAF remains a really common title. Loads were made, and it is also very reliable without signature nightmare maintenance issues that afflicted similar high watermark games (TZ, Roadshow, STTNG).
It was a game changer, absolutely superb, head and shoulders above games that predated it, hence the best selling game of all time. Despite how common it is, you pay £5k for one as it remains a good player, and earner when used commercially.
Normally rare pinball machines are flawed. The massive development costs mean that pinball manufacturers need to shift high volumes to recover overheads. Rare games generally did not sell well, so production runs were curtailed. Folk do not pay big money for sub 1,000 (?) production run games, just because they are relatively rare.
TAF Golds are perhaps unique in pinball. Rare and really good players. An early adopter of the plaque and individually numbered game/ certificate malarkey. With the kicker that there is a school of thought that the original TAFs looked and played better (distinctions introduced for the sake of it, the clumsy use of the gold plastics, random bonuses/ weird shenanigans with the mansion awards....)