Regarding "read-only projects"...
If you protect the EGP file using the file system (make it read-only, or store it in a location where those who access it cannot write to), then the project is - in a sense - read-only.
You can run the project (which modifies it with updated results) and add tasks/etc, but you cannot overwrite the original EGP file.
If you're looking for a "browse-only" mode, where you can only look at the contents of a project but not add or run anything, EG doesn't have that. We would be interested in hearing whether there is interest in that and how you would use it.
Chris