Imo, KineticPoet was correct in considering vehicles as additional types of 'armor'.. and thus I believe they should be balanced accordingly. I've always felt that Shrikes and other vehicles in T2 were, to an extent, displaced from the action; as if they were playing a 'seperate' game. This was mostly prevalent in base, as vehicles were able to interact with the 'battlefield' (ramming, blastering, moving about) while the actual players couldn't really interact with the vehicles (no mine disk + super shields = suck). It was truly pitiful how little 'skill' or 'intelligence' meant when faced with such vehicles... in that you could be the greatest player in the world, but if you don't have a uber-newbie auto-aiming faggot gun (missile launcher) you couldn't really do much to vehicles. In the Classic mod, fortunately this was changed... as lower shields coupled with faster speeds (for armors) along with MDs improved the balance tremendously.. but for the next Tribes game, I believe it could be better.
One of the greatest strengths of Tribes (imo), is the fact that there aren't any artificial limitations enforced on players... in that you can achieve just about anything if you are good/smart enough (regardless of your current loadout). On many maps you can rape gens, defend your flag/base, and cap all in spawn gear... even though it can be quite a bit easier (depending on the map) if you have a well-suited loadout. You can also kill anyone (regardless of their loadout) while in spawn gear, even though the equipped player will tend to have an advantage... the better player will almost always prevail (regardless of equipment).
Vehicles in Tribes 1 can be easily chained down, the pilot can be sniped/disked/etc.. and although they may be a bit underpowered (with the exception of owning RTs, hofs, and scout capping) they are hardly 'displaced' from the action (as they are in Tribes 2).
Obviously, the scout in Tribes 1 was designed for a completely different game (without skiing/djing)... and if it's truly necessary to include vehicles in the next Tribes game.. they should be designed with T1-like speed in mind. In which case, I'd recommend a 'hybrid' vehicle of the T1 scout and the T2 shrike. Tribes is all about freedom of motion, and the vehicles should be no exception. They should each offer an alternative method of movement (each requiring great skill to master), while retaining a semblance of balance with respect to the primary medium(s) of transportation (skiing/djing). Vehicles should be very fast, and very poorly armored/shielded... allowing great players in spawn to easily dispatch decent/average players in vehicles. Vehicles should merely offer an advantage (comparable to the cost of acquiring a vehicle: time + gens + v-pad), much like how an e-pack affords a nice advantage to a player in Tribes (but you still have to do the work yourself, and it doesn't magically protect you from better players). Thus, the 'scout' or 'shrike' of Tribes 3 should imo be very fast, have a disk like projectile (which should be powerful, as it would require great skill to use), have poor shielding (you should be able to kill the pilot), and have incredible maneuverability (instead of automatically absorbing various projectiles, you should have to dodge). Furthermore, they should never be necessary (as they were in T2 base) to achieve an important objective (such as capping...).