Thanks!
The "base project" solution is one that I had not considered...and it worked!
I didn't have a base project created, so I
- set one of the earlier projects (that had dplyr installed, along with most of the other packages) as the base
- created a new project (which uses the space's base project as the starting point)
- named the new project "base_project", and deleted all the unnecessary files
- closed "base_project" and then set it as the base project for the space
- created a new project, and voila, dplyr is installed
Thanks again!