How was he treated by the media? Did they ever have him on to discuss the politics of the day, or was he largely dismissed and/or ignored? It seems to me that he would have been able to share an interesting perspective, but he was largely hated if I understand correctly. Did he have enough followers that he would have been able to get his thoughts across? Was he still sour about the Watergate Investigation when he died? How did he feel about other political events that followed his resignation, such as the Reagan Revolution or the end of the Cold War? Was he able to sell books or do big speeches for money like other presidents after him? Did he devote his time to other causes or charities? Did he have any hobbies that we know of, like W's painting?
Immediately following his resignation Nixon was in a difficult position financially. It's what led him to accept $600.000 for the infamous Frost interviews. The $2.3 million he was paid by Warner books pretty much secured him financially from that point onwards. There was somewhat of a backlash against the memoirs however, most notably from the Committee to Boycott Nixon's Memoirs. In general the outrage stemmed from the fact that Nixon was now set to make millions in spite of his involvement in Watergate. In spite of that his memoirs were well received critically and commercially.
For most of the eighties he was fairly active in public life in spite of his association with Watergate. Even with that stain on his record he was still in demand for his foreign policy acumen. He had already written one book, Six Crises, as a sort of proto-memoir following his 1962 defeat in the California gubernatorial election, and his writings were in demand. Besides a second set of memoirs dealing with the period following his resignation (In the Arena: A Memoir of Victory, Defeat, and Renewal) he wrote numerous books on foreign policy including Real Peace, which was essentially written in opposition to what Nixon considered to be growing American appeasement towards the Soviet Union, and Leaders, which were his personal views on the characters of various government leaders he interacted with during his career. His last book, Beyond Peace, was completed a mere two weeks before his death. He also made frequent public speaking appearances, focusing solely on the same foreign policy issues that had always been his passion.
As for Nixon and Reagan, the former had fought off the latter as a challenger representing the conservative wing of the Republican Party during the 1968 primaries. Nonetheless Nixon seemed to maintain no ill will towards Reagan and even maintained an unofficial relationship with Reagan during his presidency, occasionally sending him notes and memos on foreign policies, and in 1987, following a visit by Nixon to the Soviet Union, he was invited by Reagan to a secret White House meeting to discuss Nixon's personal impressions of Mikhail Gorbachev. He was never formally involved with any functioning of the United States government however.
He also maintained informal ties with world leaders he had come to know during his time in office. This was essentially a repeat of the 1962-1968 period, which he had dubbed his 'Wilderness Years', in which he built and maintained friendships with leaders from around the world in anticipation of a political comeback. He attended several of their funerals, sometimes against the wishes of the American government, such as the funeral of the Shah of Iran. He had a somewhat cordial relationship with Deng Xiaoping and Mao Zedong. Most notably, when Deng visited the United States in 1979, he more or less forced Jimmy Carter to invite Nixon to the state dinner, because otherwise Deng would have visited Nixon personally in California.
Nixon's relationship with the press had always been bitter. Most notable in this regard is his 1962 press conference of course, the one where he remarked that 'you won't have Nixon to kick around anymore because this, gentlemen, will be my final press conference.' Nixon devoted quite a bit of time during that press conference to air out his grievances with the way he perceived the treatment he had received of the press, bitterly remarking that with all the press coverage campaigns get, maybe one or two journalists could be devoted to actually writing down what a candidate says. The role the press played in Watergate only exacerbated this.
In short, Nixon's formal role in politics was over with Watergate, although he was able to make a comfortable living as an author and public speaker, valued for his experience in foreign policy. Even his staunchest political opponents couldn't deny his expertise in that area. He had informal ties to the Reagan White House.
Most of the above was taken either from Nixon's own memoirs (In the Arena) or from Stephen E. Emabrose's Nixon Volume 3: Ruin and Recovery, part of a trilogy of books on Nixon's life, the latter of which covers most of what you asked about.
Some newspaper articles on the Committee to Boycott Nixon's Memoirs: https://news.google.com/newspapers?nid=1346&dat=19780428&id=sW9NAAAAIBAJ&sjid=BPsDAAAAIBAJ&pg=5637,7899044&hl=en; http://www.nytimes.com/1978/05/31/archives/dont-buy-books-by-crooks.html