This would be a good quick fix, and I'm ready to implement it if you are

, but I think it avoids the deeper issues.
(note: the following opinions are those of an SR newbie with about eight months' experience GMing for Kagetenshi's rigger Alex.)
The two major issues, as I see them, are the TN problem and the Sensor mechanics. mmu1 touched on the first one, and it really is a big deal: it's not hard to bring a even a big van's handling down to 1, and then the VCR-3 offsets any situational modifiers that come up. I actually don't think the VCR is at fault for this. Instead, it's too easy to reduce the handling on an off-the-lot vehicle. Drive-by-wire is the big offender here: it's quite expensive, but it pays for itself when your TN to dodge that lightning bolt is 2 instead of 5. It pays for itself again when you ram the mage. When the guy throwing the lightning bolts is a spirit in the storm clouds above you, and it's dark and rainy and some magical effect has cut your speed by a factor of six, it can pay for itself three times in an hour of play. You get similar bad results out of [Ac|De]celeration.
Sensors. Most of the problem is in the lack of specificity, I think. There's no clear definition of how the different parts of a sensor system relate to its ability to detect things, nor of how Signature is really calculated, and the parts that
are defined are often internally inconsistent. This makes it difficult to extend the Sensor rules for new situations.
Example: thermal dampers raise the Signature of the vehicle they're installed in while in use, even against vehicles with Sensors=pitiful and no heat-detection ability. Example: Sensors versus Concealment (by canon there is no interaction. Should there be?) Example: What do you do when the sensor apparatus gets covered with black paint, or freeze-foam, or a giant loogie from the troll adept? What do Sensors and Invisibility do when they interact, besides produce flamewars? Why?
I'm not suggesting a move to a more complicated system, with differing sensor components providing different modifiers against different targets. I'm saying that Signature as it stands is too abstract to be useful as a measure of an object's visibility to sensors, which forces the sensor system itself to be uselessly vague in how it does what it does.
Were I rewriting the SR vehicle rules, I'd disassociate kinds of detection systems from Sensor rating. Sensor rating would control the number of dice that you get for Sensor tests and perhaps the amount of magnification that you can muster, and would represent sophistication of the image interpretation software that the vehicle carries. Sensor tests would work similarly to Perception tests, with maybe a few Sensor-specific modifiers. Add-ons for the sensor system (ultrasound, thermo, &c) would be available, and would work like their cybernetic counterparts. Signature would be taken behind the woodshed and dealt with.
There are other, minor issues: vehicle fragility/invulnerability, the tendency of the Acceleration test to nonconsensually violate the physics fairy, the whole Ramming thing, vehicles containing other vehicles. But Acceleration and Ramming become more fair when the TNs involved are 4 instead of 2, and fragility/invulnerability has been done to death on these boards. Ultimately I suspect that
all of the vehicle rules need to be scrapped and re-written, but I've no idea how to do such a thing usefully.