Balesir
Adventurer
This is a fine mode of play, and it appeals to me, too. But the problems continue from what you identify, here.There's another option: the players can choose the level of risk they are willing to face. The DM's job in this case is to provide an interesting setting that contains various levels of risk and some way for the players to learn about that risk; he doesn't need to worry about balancing an encounter for the party. (I doubt there will be much support for how to provide information other than some kind of check. Oh well.)
As you say, problem (1) is that the system contains no mechanical support for assessing the risk of a specific route or encounter other than "roll agains INT"... AD&D actually did have some (low level) stuff for this; the Cleric's "Augury" spell, for instance. I am setting up to playtest something very similar as a ritual in my 4e game, in fact - I think it could work very well as a ritual, since that doesn't limit it to the Cleric. Problem (2) feeds straight back to [MENTION=710]Mustrum_Ridcully[/MENTION]'s point, though; if you don't have a clear mechanism for the DM to estimate how tough a particular challenge is, how the devil is s/he going to give that information to the players?