It might help to further illuminate the potential value of Gresham's Law (as applied to philosophy, or at least religion) if we could subdivide Bryan Caplan's "wildly irrational religious beliefs" into at least two categories: official dogma and "other." Then, the corresponding lack of intrinsic value and the assignment of value (in current practice or traditionally) by fiat, both aspects of Gresham's Law, makes specie and sacrament similar under this argument.

As with cupro-nickel quarters and Religion now: There seems to be very little irrefutable evidence for their value, but there is a total acceptance of quarters and a 95% agreement among Americans that we are a Christian nation, probably because doing or saying so is nearly free and the converse objectionable.

Never mind that the very notion of a Nation being Christian is so self-contradictory as to be oxymoronic. This is Gresham's Law in action - both are "bad money."

Many are offered, but few are "chosen."

I think the opposite.
Bad philosophy is necessary to define, nourish and refine good philosophy.
Plato, Augustine, Nietzsche - just to name those that readily come to mind - would they have possibly written what they did without their goal to criticize "bad philosophers" ?

It is not uncommon that the only merit of a philopher is that he was so bad as to elicit the response of a better one.
How many of us know of Swedenborg - if any - only because of Kant?

I can hardly conceive philosophy without this initial "taste" for what one likes and dislikes in philosophy.
(And, broadly speaking, criticism and confutation are mainly the attempt to affirm the "good" philosopher's taste over the "bad" 's one).

Then, of course, everybody is free to decide which philosophy is good and which one is bad...

In a related question: do bad analogies drive out good analogies?