I have work in London's East End as well as in Brighton where I live. Sometimes just going half a mile in the East End to the next job can take longer than driving 10+ miles to a job in the Brighton area.
Not only that, parking in the East End can be a nightmare and sometimes I have given up trying to find anywhere to park and left the job untill the next month.
I have 4 days each month of houses on the south downs that are well off the beaten track and during summer especially, I love it.
I've found that realistically you can charge a bit more but not a lot. Even though customers who live in these types of places tend to be better off than the average or even stinking rich, most of them won't part with more of their stash than they have to.