One of the other connotations of cashing in on something is that the thing riding the coattails is the lesser. That clearly wouldn't be the case here.
"Clearly?" How many SW movies were actually good? There are really only two of the six that are considered classics. And the original film never aspired to be more than a lightweight popcorn movie -- while the prequels' attempts to say something more substantial were hamfisted. SW has the edge over ST in production values, but certainly not in terms of writing or acting.
And really, as I said before, it's a mistake to treat ST and SW as direct competitors. They aren't trying to be the same thing. They work on different levels. TOS's inspirations were things like Forbidden Planet
, Horatio Hornblower, The Twilight Zone
, and the prose/pulp science fiction of the '40s through the '60s. SW's inspirations were things like Flash Gordon, The Searchers
, Kurosawa's The Hidden Fortress
, and Joseph Campbell.