Shield bashing in 2e is lame. Even with the Combat and Tactics rules, this is what you get:
What the hell would make shields useful as weapons? Well, after taking a look at a video from the Mosgard Museum in which viking shield-fighting is explained, I got some ideas.
With that in mind, anyone struck by a blow from a shield must save vs. paralyzation (at a +2, 0, -2 bonus/penalty for small/medium/large shields) or lose their next attack as they flinch and overbalance. Characters hit with a shield-punch also lose any dexterity bonus to their AC if they fail this save until the beginning of next round, making a follow-up blow from a sword a much more certain thing.
I think that brings some dignity to shield-punching and more accurately represents why you would ever want to do it. I have yet to use the rule in play, for I thought of it just this morning in the shower, but I am changing all shield-punching in the 10th Age to run along these lines until I determine its a bad idea.
Note: this maneuver is still more useful for higher level characters -- both because it will land more successfully and because it serves to break up a high level foe's attack pattern.