I've owned all the 'Euro' Action Masters at one point or another. Since they were released here, I had Sideswipe, Tracks, Bombshell, Powerflash, Charger, Take-Off, Windmill, Double Punch and Circuit as a teenager, and I've accumulated all the others since then (and subsequently bought and sold them in ebbs and flows countless times. I keep buying and selling Action Master Thundercrackers in particular for some reason.)
Yes, the main reason for their inflated prices is that these are G1 toys (and in Sideswipe's case, 'Geewun' G1 toys) that were released in relatively limited numbers. If people want to 'complete' their G1 collection (which many more collectors are doing now than ever before) then they're competing for toys that don't exist in the numbers of the regular US G1 toys. On the other hand, in my opinion, all the 1991 Action Masters are great toys, and the Exo-Suit/Elite gimmicks are better than those of all the previous Action Masters. So it's a bit of Column A, a but of Column B.