And another general measure for this sort of thing is to ask, "if Kant had never been born, how many extra years would it have taken astronomy to reach the understanding it has today?" The way scientific progress has accelerated with modern technology, that one is probably a particularly sobering metric! Or a somewhat different question is, what service did Kant do for his followers by giving them a correct picture of nebulae, in the absence of proof, versus just some other equally satisfying but incorrect picture?