I'd seriously think if simply putting less stuff in a bag you already have would not be better than buying another bag. I say that as a recovering bagaholic.
Otherwise check out the Tenba Mini Messenger. Or take the real messenger bag you already have. That's what many Parisians use as a day bag. You can put a camera, a map, a guide book and even a sweater for when things get cool or hot and you don't want to wear it anymore. And you can put a bottle of wine or whatever else you decide to buy along the way.
My own daybag is often the Eastpak Madison of which I have also written a review (should pop up with a google search). If I need more room it's the Tenba Small Messenger. If it's a bit more formal I use the Briggs Riley BB107 (also check out the review) which, unfortunately, is discontinued.
The Tenba Mini Messenger is about the same size as the Timbuktu but has better features and looks cleaner. Same price, too. Plus, not every dude is gonna have one.
Also look at Crumpler bags for something more fashionable.
Till