Actually, the Arsenal errata has this to say about custom sensor packages.
QUOTE (Arsenal errata 1.3.2: p. 105 Individual Sensors and Sensor Tests)
If a character improves the ratings of all of the individual
components in a sensor package, the overall Sensor rating of
the vehicle should also be improved accordingly. For the pur-
pose of improvement, sensors that do not have a rating are
considered to be automatically upgraded, when all the remain-
ing sensors in a package are improved to a higher rating.
Basically, if you improve the sensor package, you recalculate the new sensor rating. Which makes it rather easy to get a decent sensor rating. Between a decently rated camera, a microphone, a few cheap enhancements, and a motion sensor its pretty easy to hit a sensor rating of 5 or six to feed your tacnet. Even better, you know how drones get three passes? And a recon drone probably isn't going to be using all of them since its not armed? Wtih tacsoft, it can still contribute to a fight, by making use of a tacsofts Indirect Fire capabilities. It can spot for other weapons, OR make Sensor Lock-On tests for your -other- drones.
So if you pair, say, a dragonfly or an optic-x with your doberman, that doberman now has an entire extra pass to shoot people - because its not wasting simple actions with Use Sensor tests. If it happens to be carrying an Ares Alpha, it can also bounce grenades around corners that much better. Even a rating 1 tacsoft is very useful for your drones, for that reason alone.
Another thing people often overlook is how great drones are at jamming. Vehicle ECM works like area jamming, except it can go up to rating ten. Its really expensive, but an iball in your pocket can shut down anyone nearby that doesn't have top of the line ECCM.