This and the increased validation fees (therefore increased entry fees) are the main reasons against making the ride a BRM.
Indeed.
I do like brevet cards, but I like them when they are full of stamps... if they are empty (info controls + commercial) I typically bin them. For a card full of stamps, you need people at controls, which typically means you charge more, maybe offer food, given you have people there... it becomes a TLC event, which in turn becomes very popular... hence pound more pound less, making it into a BRM is totally worth it.
So it really is down to what type of event you are running.
I think the minute more or minute less speculation on average speed makes zero difference. Folks who finish 5 minutes before the time limit do it on purpose. I can't think of anyone who can cycle 400 km but struggles to keep a 15 kph average...