Restrict Users from creating + editing higher level accounts, but still able to create + edit lower level accounts
I finally Discovered the Role Delegation module, which provides the exact functionality described above. Apparently Role Assign also does a similar trick. 

Both, however, allow the assigning of multiple roles to a single user, rather than forcing a single role. This allows a user to apply multi-layered permissions to a single user. 

If there's any way to force a single role choice, it would be perfect. 

Update

I tweaked my copy of the Role Delegation module to show radio checkboxes instead of conventional checkboxes. It doesn't inherit settings like 'default role for new users', but it avoids this multi-user issue.