Remember Ted Ginn when he first came into the league? He couldn't catch a cold, yet he was always open and man, he was fast. Many years later, he became a decent NFL receiver. He was never really a #1, and he never had the sure hands of a top receiver, but he has been around awhile and done okay. He's caught some balls and scored some nice touchdowns.
Could Robert Foster develop like Ted Ginn? It certainly is possible. It will take a lot of work on his part and dedication to the craft. But, like Ted Ginn, he will bounce around a lot of teams as a marginal talent and likely won't be here to allow us to enjoy the fruits of his labors.