Trying to get the most out of WordStar, I managed to replace vdos.exe with vdosplus.exe in the VDosMac application, and it worked! I followed much of the information about setting up wordstar and vdosplus by Robert J. Sawyer found here: sfwriter.com/ws-vdos.htm.
If anyone is interested in the steps, happy to explain.
Still get the VDos splash screen though, more frequently than every three hours!
Quick follow up -- actually the splash screen only appears when I am online at work (and probably shouldn't be futzing around in DOS).
The advantages of VDos/VDosPlus for WordStar (on the Mac) far outweigh DosBox, but there are a few frustrating sacrifices -- I can't resolve the weird directory display problem in WordStar (it ONLY shows full 8.3 names; there must be 12 characters inc. the period) unlike DosBox. I read a comment that this was related to Wine that runs the Windows program not VDos itself. And WSCHANGE only works with some versions of WordStar under VDos, not all, or not after the print effects patch has been installed. I still use DosBox to run WSCHANGE.) And another mystery, although I have been able to install two laser printers (including the Apple laser printer that has more fonts!) none of the built in printers such as WS4, ASCII, DRAFT etc., are available afterwards in VDos, although they are all there under DosBox.
Perhaps my setup is now too specific, but has anyone found solutions to these nagging issues?