Currently, vehicle weapons are a bit lacking in depth, and most weapons are straight up upgrades over others. This means that when arming a vehicle, there's usually no point in fitting anything but the biggest available cannons to your ride, unless it has some kind of special ability, like ion cannons, or the quad-cannon's Accurate.
So, I've been toying around with an idea, inspired by EVE online, namely assigning vehicle weapons a rating called Tracking, essentially a replacement Silhouette value that denotes how effective certain weapons are for tracking small, fast targets. This rating would replace the attacking ship's Silhouette when comparing Sil ratings for attack difficulty as long as the weapon is in a turret/flexible mount. A weapon in a fixed forward, pilot-operated, position would could perhaps default to the ships inherent Sil rating, but would in turn only be available to the pilot. Depending on how you balance things, this could make it more useful for larger capships to actually mount smaller point defense cannons and perhaps stop turret mounted weaponry on smaller ships from being overpowered.
A rough first draft could give weapons the following tracking ratings:
Autoblaster, light blaster cannon: 2
Heavy blaster cannon, light laser cannon: 3
Medium laser cannon, Heavy laser cannon, light ion cannon, quad laser cannon: 4
Medium ion cannon, light turbolaser: 5
Heavy ion cannon, medium turbolaser: 6
Heavy turbolaser, Battleship ion cannon: 8
Concussion missiles: 4*
Proton torpedos: 5*
*never defaults to ship Silhouette.
This is just a rough draft of an idea, and not even remotely playtested, but I'd love to get people's input and see if something decent and easily implemented could be worked out from this.