I think snooker is unique in that any movement in the crowd disturbs the competitors (unlike in football, tennis etc). As spectators in most sports have to move around during the event for refreshments, fresh air, toilet breaks etc, it has to be allowed in snooker as well.....you can't expect people to sit still for 9 frames(!)
I don't think it always has to come after 4 frames though. How about, in best of 9's, having an interval when someone wins 3 frames? That is, at 3-2 or 3-1 or even 3-0? That way, no player will be allowed to run away with a match too early, and the spectators will always be guaranteed 2 frames after it.
How about playing longer matches in a single sitting too? For example, best of 13's could reasonably be played, with an interval when someone reaches 4? This could be a format for a Chinese event to distinguish it from all the others?
I remember in the Mita World Masters in the early 90's, ALL matches were played in a single session, even though the first rounds were best of 11, rising to best of 13, 15, 17 and 19 for later rounds. I think they just had a 15min interval every 4 frames (might have even been 5). There was a Drago-Griffiths match as I recall that went 9-8 and they had 3 or 4 intervals, but it was all played out without the normal break in a best of 17.