We add the expertise feats, as many as needed in CB, for all our games.
For improvised attacks and the like, I usually have the player use an actual attack power they have anyway, at-will, encounter, daily, whatever. Rogue asks me, if he can use Sand in the Eyes with his mug of ale, instead of quick drawing his dagger and attacking with it, I'm not gonna say no. We use the same stats as his dagger attack. So he does 25 points of damage including sneak attack and blinds the target with ale in the face. Works for me. I'm fine with a wizard using cloud of daggers with silverware from a table (using stats for his staff), and a fighter picking up said table and using it for tide of iron (using stats for his longsword).
As far as I'm concerned enhancement bonuses from a weapon/implement of choice, expertise, focus, etc, are all inherent, and show a character's "fighting ability". The rest is all skinning.
Side note, I would have no problem if a DM went with the lower monster defenses method.