Maybe your fuel pressure is not building up? Weak pump or clogged filter? On my non-turbo I have changed plugs about every 35-40K miles. If badly worn with lots of visible erosion of the electrode(s) the fuel economy, smoothness and power will suffer, not necessarily the starting up (though it can). If your car is a stick shift, try getting under way in top gear from a stop on a level road. You have to be gentle with the clutch. If ignition system is not good you will not be able to do this without bucking or stalling the car. Could try in "winter" mode with an automatic but this may not be a clear test. It is often the torque at low speed under load that suffers first when ignition is marginal. Another ignition symptom can be poor starting on wet days.