Having had a few days to cool off, I'm still disgruntled, but turns out I have to grudgingly admit I'm not as screwed for EWR as I had initially thought.
(There are only a couple of Hilton properties there these days: this Doubletree and a couple of Waldorf-Astoria properties.) I tried a whole bunch of different combinations of rooms, dates and points, and by making three separate reservations was able to get three nights on points at the W-A Reach for a total of about 135K, at a room that isn't the bargain-basement most basic ("Traditional Boutique," whatever that means. There's all of one photo of it online, but it's allegedly 425 sq feet... doubt it'll have a view, but we Diamond beggars can't be choosers.) I hear that property isn't up to W-A standards, but it is oceanfront and centrally located.
We're going to pay through the nose for two other days at the property - sandwiched between our two reward reservations - but will do it to get the same room type and hopefully avoid having to change rooms.
I think this is a worthwhile trick, folks - just keep trying different dates and combinations of rates & room types. The quoted rate for this room for our entire 5-day stay would have been over 300,000 HH points - but by slicing it up into separate 1- and 2-night reservations we were actually able to get decent value. Have no idea why the rates are outrageous for some nights but then back into a reasonable range for others - and that's true for some room types but not others.
Not happy about having to go to a bunch of trouble fooling with Hilton.com, but it beats having my points seem almost worthless. Another downside to slicing-and-dicing some W-A reservations: You have to put down a one-night deposit for each individual reservation. They're still cancellable, but be prepared to pay cash up front if you're, say, booking a one-night paid stay between reward nights.
Not sure if I'm going to stick with Diamond or downgrade to Gold and then parse my other reservations between Priceline, Marriott and SPG. I'm forced to admit that living in this part of the country it's hard to beat Hilton's coverage, and as of yet the devaluation hasn't metastasized to every Mom & Pop Hampton Inn in the mid-South. Sigh.