For the first time in a couple of years, I got all my equipment back online in the WSPR mode. I used to run WSPR primarilly with my little Yaesu FT-817, but this time, I chose to go ahead and use my ICOM IC-735, which isn't a really all that great at WSPR-ing: it is, after all a rig capable of a full 100W output, and even on its lowest power setting should beam out 10W of power. I've also suspected that in comparison to the receiver in the FT-817, it's a bit deaf: it simply can't hear weak signals.
Last night I left it simply listening on the 30m band. In previous attempts at WSPR, I could expect to hear signals from a couple of dozen different stations. In the last four hours, I've gotten two: NM7J in New Mexico and JQ2WDO in Japan. I think it's a receiver/antenna issue, since I'm not seeing signals in the waterfall which aren't being decoded: I'm simply not hearing them.
I'm going to move my monitor up to 20m for the day, and see how that works. But I think some antenna testing and maybe trying my trust FT-817 in its place would be a good way to proceed.