Personally, I believe that building a good defensive base on the surface of a planet should be less resource intensive than building the ships to attack it. Not because the developers nerfed the attackers, but because the attackers need engines, fuel, and ammunition for each of their ships. The defenders will need ammunition and electricity as well however by its very nature bases should have an abundant supply to defend its self. I agree with the original poster that unless the enemy overwhelmed you with something resembling a Star Destroyer your structures should not be easily destroyed with something like a speeder. (keeping with Starwars references)
Explosives yes, cannons yes ,machine guns your character shoots no.
With a proper design of walls turrets and other defences, you should be able to stand your own against similarly power entities. As mentioned before, if you attempt to combat much stronger opponents than yourself then nothing should stop other players from destroying what you have built. Unless they try to destroy your reinforced wall with a machine gun.
The only thing that would piss me off is if characters are able to dig at an unreasonably fast rate. Allowing them to tunnel into you base quickly within minutes, passing the defences you laid because they dug 100 units down went under your base and used the mini map to guide them into the heart of the base.