His first public infiltration took place in 1977, when, dressed as a janitor, he sneaked into the Los Angeles County Museum of Art and exchanged the gallery wall-socket plates with his own hand-painted versions.

Vallance's over 80 performances have often involved interactions with foreign dignitaries, including audiences with King Taufa'ahau Tupou IV of Tonga at the Royal Palace in Nuku'alofa, Pope John Paul II at the Vatican, and Icelandic presidents Vigdís Finnbogadóttir and Ólafur Ragnar Grímsson at Forseti Höll in Reykjavík.

In the early 1970s, during the Cold War, Vallance corresponded with government officials in the Soviet Union and Red China, trading political badges with communist party leaders.

Also in 1983, Vallance appeared on NBC's Late Night with David Letterman to discuss what was then his best-known project, Blinky the Friendly Hen, in which he purchased a frozen chicken from a grocery store and buried it at a Los Angeles pet cemetery, and Cultural Ties, a "mail art" project involving the exchange of neckwear with such international dignitaries as Anwar Sadat, King Hussein of Jordan, Austrian president Rudolf Kirchschläger and dozens of others.

In 2000, he was conferred with the royal title of Honorary Noble by the Tongan National Center, Nuku'alofa, Tonga, and also received a Distinguished Alumnus Award from Otis College of Art and Design, Los Angeles.

Since 2003, when psychic medium Dorothy Maksym identified Vallance as being the earthly spokesperson for the disembodied spirit of former US president Richard M. Nixon (The Haunting of the Presidents, by Joel Martin and William J. Birnes, Signet), Vallance has taken an interest in the paranormal, contributing stories to the UK's Fortean Times and leading ghost tours of the Nixon Library and Birthplace in Yorba Linda, California.

Vallance's paranormal research projects include Bigfoot, the Shroud of Turin, the Holy Lance, ghosts of dead US presidents, the Ravens of the Tower of London and the Loch Ness Monster.

For a project at the Frieze Art Fair in London, Vallance assembled psychic mediums to channel the spirits of five famous dead artists: Leonardo da Vinci, Marcel Duchamp, Frida Kahlo, Vincent van Gogh and Jackson Pollock.