I don't think Super User is too broad, but:
- The Opensource alternative proposal may be way too narrow. Would I go there only to ask for alternatives to X paid application, or would I also be able to ask questions on how to use the open source alternative? If it's the former, then it's too narrow. If the latter, then it duplicates a lot of the purpose of SU.
- The Computer hardware proposal is about half of what Super User is for, per the SU FAQ, so I agree that it would be too close to duplicating an existing site.
Also, I think a lot of the questions that did make Super User feel a little bit too broad are now handled by more focused sites like Ask DifferentAsk Different, Ask Ubuntu, and Unix & Linux.