The earnings from selling Stormtroper merchandise (and thus the damages Ainsworth can claim) have increased substantially in the 25 years since Lucas started doing it. Lucas is clearly in a more vulnerable position now than if Ainsworth had sued him in 1977.

Doesn't work that way. He can claim what it was worth 30 years ago, the same as everybody else got when they claimed it 30 years ago (still a fair chunk of money). No reasonable judge is going to give him what it's worth today. A mere increase in value is not sufficient for laches; the essential requirement is that the losing party must have made different decisions as a result of the delay, and that those decisions have left them in a worse position.

If Lucas had believed that he owed no royalties to anybody and then sold the rights to somebody else (who would now sue him for screwing up), that would be a case for laches - his position has been harmed by the delay. If the royalties would amount to more than it was worth then he could claim he wouldn't have gone ahead with the project if he'd known about this in advance, and that would also be one. But there's nothing like that here.