After giving this some thought, I believe these steps will lead to improved selection tournaments. So these are my suggestions.
The first thing would be to cap the minimum fide rating for participants in selection tournaments. If the field is essentially strong, it will discourage "ducking" as a tournament strategy.
The second is to implement a ban on walkouts in the next or subsequent selection tournaments as this affects the tiebreak of their opponents.
These changes will ensure that those who make it will be battle hardened and ready for National Representation.
A Challenger Cup on the side should satisfy the needs of all. Maybe we can add a clause to say that the winner of the previous Challenger can move into the main event the following year. This should encourage players to increase their ratings if they want to vie for National Honours.