Ya'll think it's overkill to encase the exploration counters in nickle-sized coin capsules? I'm concerned that over time they will become marked through play handling.
If wear and tear does occur to the point that you can tell which tokens are which when face down, substitute a different token (I'm sure you have or can think of general-purpose bling to use here) and put all the exploration tokens in a bag. When a player hits an exploration spot draw an exploration token out of the bag.
I actually already do this, not due to wear and tear concerns but because I hate shuffling tokens/tiles and trying to keep them face down.