Personally I prefer to have separate projects for enterprise and project-level. This allows read access control of content in the project level area, so that not every project can see the contents of another project unless they are explicitly added.

For example on Jazz.net there are a number of private RM projects which for several reasons are hidden from the wider jazz.net community but there are also public projects where requirements can be referenced by everybody.

Follow this link for the public projects https://jazz.net/rm/web and look at the CLM RM project for the lifecycle scenarios we are developing publicly.

The negative side of separate projects requires managing several projects and baselines cannot span projects.