I've played in an IDP keeper league for 20-ish years that adds a point for every 15 return yards. It has some other unusual scoring settings as well... 1.5PPR, and .25 per completion for QB's (not to mention 6 pts for all TD's). So, offensive scoring can get pretty high. Meanwhile, defensive players are the opposite (1 pts per tackle, 0.5 per assist), so the average defender in any given week might score 5-8 points.
As mentioned above, guys like Hester can definitely have a lot of value, especially in leagues like mine where 75 return yards in a game can essentially double their typical points. Of course, the problem is that finding guys who play regularly AND return kicks is pretty uncommon. And, with rule changes over the years, there are just less and less returns than there were 10-15 years ago.
I remember winning that league maybe 10-15 years ago with Josh Wilson as one of my DB's. He was one of the rare starting CB's who also returned most of Seattle's kicks. I wouldn't say he was a league winner (because, again, DB scoring was relatively low), but having a guy who scores 10-12 PPG when everyone else at his position is scoring half of that did make a difference.
On offense, it's even more rare... Even guys like Dante Hall (one of the best return guys in the past 30 years) barely scored enough to make himself fantasy-relevant. He had games where he made an impact outside of kick returns, but not consistently enough. That said, if you can find the occasional starting WR who also returns kicks, it can be a game-changer. Of course, those situations are usually short-term because teams typically don't put starters on special teams for long, unless they're super talented at returning kicks.
