Bases don't have little health bars above their heads, just like ships. I prefer the "chance" aspect of bases.

One thing I have thought of though is maybe, while your base is under attack, the members could contribute energy or something to increase a single chosen attribute of it (shield capacity, attack, defence). It'd be a small boost, but if the base withstands the attack the "top contributors" get the badges that the other legion would have got if they'd destroyed it.

Adds some more control to base defence, and just while I'm thinking, the boost could scale with current raw attack/defence (i.e. it'd take less energy to have the same % increase with a base with a smaller attack.)