Hi Susan
Don't know your specific commuter situation, but when I lived in Portland and Chicago and commuted, we purposely used cheaper bikes if we had to leave our bikes outside a building when we worked because of the theft problem. Actually knew some guys who purposely made their bikes look cheap and junky to avoid attracting attention from bike thieves. On the other hand, if your able to store a bike, inside, when you work, use any bike you want.
I'm all flat bar bikes, now, but have ridden drop bar bikes, too, for many, many years. I've just found it too hard to switch back and forth between the two bikes because they use such different riding positions. That, and I'm also a mountain biker, anyway, so using flat bars for all my riding is very practical.
I'm a big fan, though of wider tires for all my bicycling. I'm sure those 28mm tires are fine, but going even wider will make for a more comfy ride, especially on gravel. 35 or even 40mm tires won't slow you down much, but will provide an extra measure of safety on rough or loose surfaces. You don't have to go as crazy as I do - my narrowest tire bike is 2.25" - but I would recommend exploring wider than 28mm, at least.
I'm a big fan of Surly bikes. They're all steel and rugged as a bike can get and set up with basic, but durable components. Won't cost you a lot, either. A Surly is no racing bike, for sure, but if you want a bike that will always get you there and back, no matter what you encounter, Surly is a great choice. They'll last a lifetime of hard riding. They do have a few drop bar models, but most of their bikes are flat bar bikes. I know the Surly line, well. Have four of their bikes and they get ridden hard.
Since I'm a steel bike freak, another great line of bikes is Salsa with their steel models, though they are mostly drop bar bikes. The Fargo and Vaya are great choices for do it all bikes.