What if instead of easily-destructible vehicles or invincible vehicles, you find a middle ground that has some degree of strategy?
Say your standard Warthog has 100 'health'. You drive in towards the enemy base and they tear it apart, to zero health. Warthog explodes, everyone is ejected and has their shields popped (but they're not automatically killed) and the vehicle becomes unusable. However, any player can walk up to the dead warthog and repair it (same button as flipping it). Once the vehicle has a set amount of health repaired (say, 20) it can be driven again.
As a bonus, the passenger could have access to an on-board repair system, so instead of shooting he can be fixing the vehicle as it's driving around. Not so fast that he can keep the vehicle up through heavy fire, but enough that he can bring it back up a little between strafing runs. This comes at the cost of being able to shoot, so it's not something you'd ever want to do under fire (in fact, to keep it from being abused, it could automatically be disabled if you've been damaged in the last 3 seconds or something).
Throw in an Armor Ability or Specialization or something that increases how quickly you can repair vehicles and you've got something to play with. Maybe even a passive ability that auto-repairs vehicles you're in or increases their maximum 'health'.
Might be an interesting strategy to leave enemy vehicles with 21 health and wait for some schmuck to hop into it for a quick and easy shield-pop.