Nicko71:
When you lack speed, more kilometers are not likely to help.
300-400 km's is plenty, especially if all you are doing are crits which are the shortest type of road races.
Focus on speed. You could ride 700 kilometers a week and none of that training would help you hold 60-70 kmh for 20-30 seconds at the end of crit.
Work on your speed. Use a cadence meter. Sprints done right are at least 120 rpm, often a lot higher. Work on legspeed on a trainer, and sprint outdoors if possible.
If you have good legspeed, you should be able to hold 120+ rpm for 5+ minutes seated without bouncing, and max out over 200 rpm for a few moments. If you are maxing out at 140 or 150 rpm, you have a lot of work to do. The good news is legspeed improves rapidly with proper training.
Good luck!!!