Mike Jones, who has a forthcoming book, told The Denver Post that several people shook his hand during the visit Sunday and told him, "God bless you."
"I had read a lot about the church, but there's nothing like seeing it for yourself," Jones told the paper. "It wasn't to rub anyone's face in it by any means. I was wanting to get some perspective, to see where they are coming from, what the magnet is."
Haggard resigned last year as president of the National Association of Evangelicals after Jones alleged Haggard paid him over a three-year period for sex and sometimes took methamphetamine during the encounters.
Haggard then was fired as pastor of the 14,000-member New Life Church. He publicly admitted in November to unspecified "sexual immorality."
In an apology to the church, Haggard had urged members to forgive and thank Jones for exposing deceit. Church members invited Jones to the church several times.
Jones visited on Sunday with members of a New York-based theater troupe, The Civilians, who are researching a project on evangelicals. Church leaders knew about the visit beforehand.
Associate pastor Rob Brendle saw Jones in the foyer.
"I told Mike, 'I don't want to impose my religious beliefs on you, but I believe God used you to correct us, and I appreciate that,"' Brendle said. "The church's response to him was overwhelmingly warm. One of the wonderful and enduring truths of Christianity is to love people the world sets up to be your enemies."
Haggard and his wife, Gayle, completed a counseling program in Arizona and are back in Colorado Springs, Brendle said.