I find it incredibly unfriendly that someone would want to make a 'premium only' cache for many reasons:
1) The hider would have less logs.
2) It limits new cachers involvement in geocaching.
3) It could keep a Tb from going to hands that could complete its goal.
4) The cache condition can not be commented on and could ruin it.
5) It stops enjoyment which is what geocaching is all about.