Thanks for your feedback, gazumped. You've given me some more ideas.
I didn't think of emailing, because my use case would sometimes be in places with no cell service...
Share to Evernote... didn't know about this one, and it might not be too cumbersome... a shortcut on the desktop to the folder where the screenshots are stored, together with sharing to Evernote, works pretty well if starting a new note with the screenshot.
Neither of these, as you note, work for adding a screenshot to an existing note. And that was my reason for asking for a feature... Yes, the ability exists to add a picture or file to an existing note, via the paperclip... but to do so requires navigating through the file system to find the folder where the screenshots are stored. The paperclip pops up a menu of options, file, photo, video, audio, etc... an extra item in that list for "screenshot" that went directly to the screenshot folder would be helpful.
In experimenting with the paperclip options, though, it seems that somehow it "knows" too much or too little about the files in the Gallery area: I see thumbnails of files that were deleted days before, and no thumbnails (maybe a broken-link sort of icon/thumbnail) for other files, and can't see thumbnails of the newer files that are there now. So this isn't particularly friendly, and although maybe would suffice if it were actually showing thumbnails of the current files, starting the navigation in the screenshots directory would be a nice addition: or maybe this could be generalized... and allow user specified starting points in the list of paperclip options... while I'm hot on attaching screenshots, other people may have other directories from which they wish to quickly attach files to Evernote.notes.