The current power-gen costs for cloaking seem quite balanced to me (a pilot who depends on cloaking and jamming).
Cloaking costs 100 energy per second per block, and jamming is 50 energy per second per block, so in total 150/second/block. In order to produce this much power, it is essential to use the dimension bonus. This can be achieved by long lines, 3d crosses, or combinations thereof. To keep down size you can use multiples of these, but a single larger line or cross will be more efficient.
These dimension bonuses, however, cap at approximately 1 million regen, meaning that it is impossible for capital ships to cloak indefinitely, and difficult for them to cloak for a long period of time. On small ships, well-built reactors as mentioned above will give enough excess energy for thrusters (Which also are more efficient in lines or crosses, FYI), weapons, shields, and the cloaking energy for said systems.
Weapons can be optimised for greater DPS by using many small arrays, but these will have less range and slower projectile speed. Shields are generally limited (This is good, because cloaking and jamming is, in itself, a defensive system), meaning ships are very fragile in prolonged combat.
Anyway, the point of all this text is that the cloaking system works well (I just pointed out the varying things that let one build effective cloaking ships), that it is, indeed, balanced to prevent cloaked capitals, and that the energy cost acceptably forces cloaked ships to be fragile and well-designed, usually with no hull or aesthetic blocks.
EDIT: I was missing a full stop.
