Tom Buckley has special and super natural powers. All of the strange things that were happening to Buckley throughout the movie were happening because of his own powers and not Silver's powers.
All the strange happened that happened to Buckley such as the dead birds, the vandalized laboratory and the explosion of electric devices were happening because of his own powers.
Simon Silver was a fraud and none of his super powers truly existed. Silver was just good at deception and that's why he seemed genuine to people including investigators.
Silver wasn't blind but he was just faking it. Buckley made that clear when he threw the coin at him while he was shocked. Silver's reflex action has proven that he can actually see.
Buckley managed to expose silver in the presence of a large crowd and all people knew that he was a fraud.
Margaret's death was a natural death. It was not Silver who did it since the man doesn't have any kind of special powers apart from his ability to deceive people.
The reason Buckley was investigating people with paranormal powers is that he wanted to find answers by connecting with other people who have super powers.
A part of Buckley wanted him to became a psychiatrist because of the good career opportunity but another part wanted him to continue such investigations to find people like himself.
In the end of the movie Buckley felt bad about not letting Margaret know that people with such super natural powers truly exist. This was clear in the letter he wrote to her after her death.