Vindicated by History/Comic Books

X-Men wasn't a particularly strong seller in the 60s, and in the early 70s the title was languishing in reprints... until someone at Marvel noticed that sales were going up, and decided to revamp the series. The revamped title became Marvel's biggest seller.
Jack Kirby's New Gods titles sold poorly (though there is some controversy about just how good or bad the sales figures were at the time, and how much of that was due to a line-wide price hike and format change). Since then, Kirby's work on New Gods, Mister Miracle and The Forever People have become widely-acclaimed as among his very best, with characters who have been used again and again, in multiple media (e.g., Superfriends, Justice League, and Smallville).
Gotham Central sold poorly during it's monthly releases (Possibly due to it being a Batman book that rarely featured Batman). Though it has now found popularity being sold in hardcover and trade paperback.