Various posts in this thread talk about the old days. No one on thread seems to know one thing about what I would consider old days. Old days would be when field limit in a category at Superweek would be 200 riders. Start the Cat 4s two minutes before the Cat 3s and you now have a field of 400. And most races would be beyond limit anyway. And yes, it would be possible to have 400 to 450 riders on course and have no accidents. When accidents did happen it was invariably road rash or collarbone. The complex injuries in today's crashes did not occur.
At the Northbrook track the junior field would be 30 to 50. Possibly one rider would line up in the "participation" category, the rest were there to race and they did. When Superweek was in town there would be 80 to 100 juniors. On regular track nights basically crashes did not occur. During Superweek the juniors could be a little dicey. But when someone fell the norm was pick yourself up, check your bike, line up for next event. It would happen a kid would go down and be back on bike so fast the ref would grant a free lap. There was no ambulance parked at the track. Why would there be? Years went by with no injury of any significance.
The senior 1/2 field was bigger. Usually about 60. During Superweek it could be twice that. Not sure the Northbrook track could even fit that many now with everyone riding massive gears. Normally zero in "participated" or "just training" mode. Racing in normal gears of 46x14 to 48x14 meant fast accelerations were possible. Riding very close was possible. One very normal sight, esp. in turn two, would be a pedal (Campy) taking a dozen spokes out of the front wheel of rider above on banking. Rider who just lost a dozen spokes would normally bring bike to safe controlled stop and everyone else would get around with no fuss. Put on a new wheel and race again.
Skill level was not in same universe as what is seen currently.
Can this ever return? Doubtful. Two technical factors would help. One would be gear restrictions. I can hear the howling already. The second would be some sort of control over use of silly and extreme time trial positioning in mass start events. Best possible control would be a years suspension for any fool enough to appear on start line with a position that put all others at risk. Since everyone who purchases an expensive bike or who pays a coach is prima facie assumed to know everything about bikes this is not happening. Coaching in old days was always free. Best coaching is still free today. When coach was a guy who had won 34 professional six day races, at a time when six day was the highest paid pro sport, no one questioned coach. There were no aberrant theories. Everyone on same program.
Old days were when Belgium sent young riders to Chicago for finishing school. Old days were when Dag-Otto Lauritzen as captain of Norwegian national team requested downgrade to Cat 3, and then wins Pyrenees stage of TdF ten months later.