Well, again, $1,500 a week is apparently the salary for an additional performer, the "core" performers are principal, so of course they're going to earn more because of it - I think the sexism angle was kind of twisted into it for the sake of drama . . . unless there's evidence otherwise, it's quite possible that even male additional performers are probably also making $1,500 a week, depending.
But hey, that's still an improvement from what Jim himself would pay: after all, when Caroll Spinney was first hired, Jim admitted he really had no knowledge of salaries and as such, only offered Caroll $200 a week - even in 1969, that wasn't a lot of money (especially when he made that a day in Boston working for Bozo).