The highlight of a meet for me are the races - it would be a great loss to drop from 3 finals to an all-or-nothing 1.
Personally, after making the commitment to drive to a round for a day's racing it doesn't matter if the meet finishes at 4pm, 5pm, 6pm or 7pm. It's all about getting the best VFM out the day IYSWIM. So I don't understand why there's a discussion about getting finished earlier than we presently do
As for the problem of repairing/preparing cars between rounds etc being eased if there were an increased entrants and therefore a greater number of heats (say 8 rather than the current, typical 6 - as Derek mentions)... Well, in that case why not just introduce the same time gap at the end of a round of heats/finals artificially?? Simples.