After days of (ironic) silence, suddenly there's lots of excellent suggestions. I went with MrSmith417's suggestion, which is an app (not a widget) called "Silent Toggle" by Scott Keller. There are several Silent Toggle's in the Market, but the rest seem to be widgets. Because this one is an app, it uses no power and can be added to the stock lockscreen. It gives us back what we had on the OG Droid, except it leaves you on the homescreen, unlocked after you swipe. Still, I call it close enough.
(Edit:? Whoops, I just realized there's one other difference: you can't tell from a glance at the lockscreen that the ringer is on or off. You must power up and look at the notification bar. Redit: I'm an idiot -- the notification bar is at the top of the lockscreen. You can see the ringer status there.)
Since we already have a customizable lockscreen, I decided to forgo the installation of WidgetLocker. The latter does seem to have some advantages over HTC's but it may have some downsides, as well, such as possible increased power drain.