I say go into Scapa. You should do it at least once. You might find a cruiser or something. It's a once-per-career kinda thing. I cheat and look up the ship dates in the SCR layer and find out if anything's in there
....it's a serious pain in the arse to get in there so I don't go unless it's worth it. Lock Ewe is also fun but it's a bit hairier to get in etc. At some point you'll find out that it's much easier to catch a BB at sea than in port.
Kb