I think that the Washington Post's (and LA Times) major contribution was from July 1972 to March 1973. This was the period during which the scandal could have been buried. After this period the resignations started and the Senate hearings occurred - as the article points out.

When considering Felt, it has to be remembered that he was convicted (but latter pardoned) for illegal spying on members of the public, which also included illegal entries.

“Felt was one of the architects of the bureau's notorious COINTELPRO domestic spying-and-burglary campaign. He was convicted in 1980 of authorizing nine illegal entries in New Jersey in 1972 and 1973 -- the very period during which he was famously meeting Bob Woodward in a parking garage. Only a pardon, courtesy of Ronald Reagan, kept him out of jail for a long term.” http://www.editorandpublisher.com/eandp/search/article_display.jsp?vnu_content_id=1000944446

It is most likely that Felt was not acting independently when providing information to the Washington Post journalists, but was merely acting as a representative of the FBI, which wanted Nixon’s removal or containment.

Probable reasons for this:- Nixon had established his own secret investigation agency in 1972, and then made major cuts to the FBI’s counterspy budget in 1973. Apparently both had created considerable “tensions” between the FBI and Nixon’s White House administration, but of course the FBI was the more powerful of the two at that time.