I have a problem with this too, and although I'm pretty adept at running something on the fly since I've got most of the classes and a decent number of magic items memorized or in formula, my pet project lately has been making a sort of campaign monster manual.
I make full monster-manual-style write-ups for average city guards, elite city guards, skilled and master assassins, sample members at various levels in the mage's guild, that sort of thing. If I know some kind of monster has a particular life-cycle or a particular area is well-known for that kind of monster I'll do an advanced/leveled version of that monster, along the lines of the Troll Ranger or the Displacer Beast Packmaster.
As I get further along in this project, I'm finding that I can easily scale these full write-ups up or down two CRs or so and not get that sense that the character is vague and ill-defined I get when completely improvising.
And really like the "typical dwarven defender" and "typical gnome illusionist" stat-blocks in the Races of... books. I've been stealing liberally from a friend's copy of them.