Winning a big challenger will earn you 125 points, that's half of winning a 250. That's too much imo.
But if you compare the prize money then the difference is a lot bigger: 18k $ for winning the biggest challenger (< 10k $ for the smaller ones) vs. at least 66k $ for winning an ATP 250 (Belgrad), and up to 177k $ in Doha
. So that's at least 3.5 times as much.
So I think most challenger players only play these tournaments to get enough ranking points to qualify for ATP events. Because that's where the big money is, and where you also get more spectators and TV coverage (thus more money from sponsors).
As a comparison: Last week Berlocq gained 10.8k $ for winning the Buenos Aires Challenger. At the US Open he gained 31k $ for beating Pere Riba in round 1 (another good example of those clay courters) and then providing cannon fodder for Novak in round 2 (he probably gained some extra money from his sponsor because the match was on center court).
I guess if you ask Charly "what do you prefer: Spending a whole week at a small clay tournament to win 10k $ or playing two Grand Slam hard court matches and getting double bagled by the world no. 1 to win 30k+ $?" he would probably chose option 2.