OK. VSS is a must for real idle system... Maybe not so accurate, but is car moving or not... Why do I say this? Because all cars have the system that rises idle rpm when the car is moving by 400rpm, and when it stops, it lower it to origin idle rpm...
Why is this important? Because of possibility that the engine would stall if you press the clutch on lets say 100km/h and rpm falls (forced induction of air in car movement)..
Also VSS is important to launch control, that would automatically turn on and turn off... Well, if the 2 triggering algorithms are problem, we could do this by simple daughter board that have another small AVR (like piggyback) that would inform VEMS of current vehicle speed over serial port or SPI, or something...
What do you think? This daughter board could also act as board computer, measure trip times, average consumption, current consumption, measure acceleration times, etc... I could do this daughter board myself...