Any kind of activity (redemption or stay) will reset the expiration another 18 months (more or less) in the future. I note the peculiarity of their expiration dates -- are they always the 29th of the month? It appears that sometimes the resulting new expiration date is a bit more than 18 months in the future, sometimes a bit less.

In any case, I decided (in the interest of preserving most of my 24K points), rather than exchanging some of them for airline miles, gift cards, etc., etc., to simply make a 500-point donation to one of the charities on the list. The new expiry date posted immediately after I did the transaction, and I breathed a sigh of relief. (Miles exchanges, for example, require a minimum of 6K points.)

(Too bad about the devaluation but oh well.... at least my devalued points are mostly still there and I have some time to use them and/or earn more.)