I have some ideas, but currently I have just started playing with ping sensors ,the mail man was good to me today.
I will play around a bit and see what I can come up, I want to build an autonomous tank so it fits in.
The big issue I see with the small servo movements, is sort of a constant left/right turn effect if the the range and time is too small.
If your current code gets you down halls pretty centered then perhaps the problem is more defining a minimum distance. So if we are with in X distance on the left side adjust to steer right a bit and move forward. You have a forward arc set up it should be possible to tweak the settings to curve away from or around obstacles. Which is what you want to accomplish in general terms.
Let me put some thought into this, I need to scrawl some stuff on paper and scan it so it makes sense. I can see in my mind what you want to do, but it is the end of a long work day and I keep coming up the gibberish.