Can you continue to get exp if you fight more then one Wendell in a day?

You wont earn any of the normal rewards. But I believe that you can still earn Exp for your heroes in the rallies but only if your APC is involved in the fight.

If you start the rally you will be the first one to fight the Clown and will get some (or all) of the kills / damage to the enemy. If you are the last to join for example and the other players finish of the clown before your turn to fight then you will not earn Exp. You can check the attack report mail after any rally to see what damage your APC did.