I'm at uni now, so I'm not sure, but the "show ships" option on the minimap turns on/off starbases too, right? (never bothered turning it off.) If that's the case, they could set resources at the same level as stars (i.e. always shown), and if you have "show ships" selected, then it'll show a starbase on top.
So you could easily see which starbases are parked on top of resources across the galaxy by turning the show ships off/on for a sec. Of course, you still have to find them before that happens.
The last seen idea makes sense, especially for starbases. It's pretty silly that you can see every single ship defending a planet, but you can't remember where a starbase was