I think it's still the best of the 3 superweapons, even nerfed, especially for the VL.... the more I play a VL "death fleet" style, moving my capital to my titan and stripping planets as I use them, the more Kostura becomes a nightmare for the enemy. I'm not using it for pirates... a proper fleet can take down a pirate base no problem without the cannon.... no, the Kostura becomes lethal because it gives you the ability to bypass a fleet, and go straight to the heart of your enemy... the more or less undefended central planets...
Once it's researched I only need to own one planet, buld a cannon and phase gate, nail an undefended planet with a cannon, preferably one rich in resources, jump in and take out as many structures as you can.... then either use the VL titan to open another phase gate and get out fast, or wait for the enemy to haul ass back to try and stop me.... either way it's a great way to leap-frog past an enemy fleet and cripple an enemy's resources, even steal an enemy planet and strip it so they can't use it again....
My opinion, when used properly, VL is the best race ever if you like to play really mean and evil! hehehe