While this sounds awesome, if ALL random quests worked exactly like that, they would quickly turn into "Oblivion Gates" - very repetative, predictable and stale from a metagaming standpoint.
So how about allowing some variation? Make sure the player knows this quest he is getting is given to him by the character because the character thinks the player might be able to handle it himself first of all. "Well since you a leader of the theives guild I'd thought you'd be the perfect person for this quest I had in mind blah blah blah...". This is important so these kinds of quests feel natural, not forced, and the "level scaling" feels like it logically belongs. If you don't do that, it'll be easy for the player to break into the 4th wall. "Oh great, another random quest and of course the challenge is the same!". If you introduce quests in a seamless manner such as that, those circumstances become much more belivable.
On another note, allow variation with the difficulty too. I'd like to get a quest from a kid or someone who is really oblivious to who I am, and then the dungion ends up being 5 or so levels easier than my level, or perhaps 5 or so levels harder.
Imagine going on a random quest, only to find a few creatures in there that really exploit your weaknesses and are pretty tough? Would be a surprising challenge and if you can't succeed then you can come back to it. If you do something like this though I suggest making it so only one "random chance for extra difficulty" quest can be aquired at a time, simply to avoid constant frustration.
Ideally, the random quest system as a whole should be designed with unpredicability in mind, and follow some kind of "difficulty curve" the more and more you do. Think Left 4 Dead, how if the game thought things were going easy and "on course", they would suddenly throw in a big challenge for you to deal with.
If random quests were always "to your level, with a few weaknesses exploited" then things will get very repetitive, very 4th wall breaking, and in turn make no one want to do them from a gameplay (and immersion) perspective.