Silver tokens have become a lot more common as rewards. They are barely worth anything to higher level players. I have suggestions to make them more exciting.
(1) Allow the ability to exchange a certain number of them for gold tokens or other items. Maybe 10 silvers for 1 epic hero token.
(2) Add some special heroes that can ONLY be summoned from the regular silver token summon. This will add some excitement and incentive to use those tokens for players of all levels.