I think the accepted figure for Stonehenge (including the fence-peerers) is about 2700 a day so Knowth is a persuasive model if it works there. Fifty shuttle buses a day (or even 150 on a very busy day) seem a pretty innocuous price to pay to get rid of all the crud. After all, they'd just come, then go, not hang about in huddles.
In the Stonehenge context there would be less need for set periods for visits as well. It could stand a few hundred at any one time, especially if people could be persuaded to wander the wider landscape (which disgracefully few do at present apparently).
