If I recall correctly, the original AR-15 had neither a dust cover nor a forward assist. For me, the dust cover is more useful for admin /daily grind issues than in actual firing / deployment of the weapon - ala the dust bunnies and Cheeto crumbs mentioned in my OP.
We "cruiser carry" all our work M-4's with empty chambers when stored in vehicles and I can't recall the last time I used the forward assist.