Full match books are worth more than match covers and unstruck are worth more than struck. Your "Feature" match book is worth more than a regular book but a full, unstruck one is worth more. Front strike is usually worth more than back strike.

My Nevada casino match collection consists mostly of covers because it is easier to store. I have 22 different Dunes which I think is about average?

This is a matchbox not a match cover:

Mark Cotton has an excellent website on viewing Nevada casino front strikes:
http://ia310120.us.archive.org/1/items/NevadaCasinoFront-strikeMatchcoverGuide/MATCHCOVERS103.pdf