I think it's universal that ships which are meant to be spammed must have the build message toned down.
Personally I think that it does not even need to have a voice. A sound effect would do, like a whoosh launching sound, and then it should only voice if I am looking at the gravwell where it was built, otherwise it just becomes noise.
Another problem is that being so readily lent to a 'spam unit' role, micromanagement should be kept at a minimum.
There should be an 'auto-build' mode which makes it easier to replenish their numbers without having to worry too much about clicking on the build button hundreds of times, or at all.
The game always knows each planet's income, and the global economy as well. Corvette production could tax the planet's production (-i credit/sec, one corvette every X seconds) and spawn automagically. There could be 4 production rates for corvettes available for the player: none/low/medium/high, with varying credit production penalties.
Corvettes for each race could have a penalty on a specific resource, credits/metal/crystal.
To make it possible to turn on/off auto-build, the planet would have to have a dedicated button, instead of having corvettes in the same build list as frigates.
Queue-clicking should still allow to 'rush-build' more corvettes to replenish their numbers faster, costing additional resources.
By tying corvettes to planets, another possibility which comes to mind is to limit their supply by the number of tactical slots each planet has, instead of costing fleet supply. But that's completely optional. It could solve the 'too many corvettes bogging the game down' - if the corvettes have no warp drive at least.
What could be an innate ability (for all or an advantage for a faction), or a tech (for those who do not have it natively) is the ability to build Corvettes without a frigate factory. If you own the gravwell, you can build corvettes in it (planet surface).
I also think corvettes should have a good chance to dodge enemy fire, at least as a tech.
At last, another option is to have carriers able to build corvettes instead of fighters/bombers as a third option.
The new capital ships should also have the ability to build corvettes as one of its skills (makes sense only if the corvettes do not become a third option for carriers), so that they can be deployed behind enemy lines instantly.
Pirates should have a pirate corvette and fighters/bombers, but they should have by default an economy-crippling behaviour, not a suicide maniac behavior (unless it's a kill-em-all bounty mission).
The pirate corvette would have at least a ship engine disabling effect, to stop trade and refinery ships. Probably weapon crippling as well, so they can go about their business with less interference.
They should target resource asteroids, refineries, trade ports and trade ships instead of star bases etc. Pirates should destroy all economy resources on a gravwell and, if there is still bounty, jump to another.
Stronger pirate raids should attack several gravwells simultaneously, instead of dumping a fleet in a single planet.
