I think the best way to balance out all the aspects of combat is to make everything combat related reliant on a power-source. Ie. if things like turbo lasers, and shields required a reactor of sorts, and possibly supplant fuel powered engines for reactor powered engines too you'd have to take into consideration the size, weight, dimensions of your ship as you're adding in turrets or creating your shield grid. If you spam turrets, fine, but you'll be shield-less while you're firing because they're using up all the power. I feel this would help to balance combat significantly.
Additionally, making power consumption the primary factor in combat, really emphasizes the advantages that planet side emplacements should have over ships/space fleets.
