When it comes to ranges beyond point blank or short I ask for a perception or reasoning roll to judge the distance. The better the roll the more accurate an estimate I give the player but it is still an estimate and yes we have had spells fall short of their target.
That's an excellent idea. I never thought to do that. I (we) always just gave the players the benefit of knowing the distances, and gave them all their bonuses, but I love this idea of the PC trying to figure out the distances. It certainly seems to be more realistic. I've had to guesstimate distances when laying line from a hydrant to a fire and there are times I'm spot on and times I'm off by a shot. Depends on the adrenaline, the impetus, the emergency, as to how well I gauge my distance. Why not have the PC's in the heat of combat subjected to making a snap guess at distance?
My players may not like the change to the gameplay, and if they don't I'll just say it was YOUR idea.