In the northeast, it is typically very difficult to sell a house with knob & tube because the buyer will find it near impossible to get homeowner's insurance. It is a potential fire hazard due to (1) people tying new wiring to it and (2) people packing insulation around it. If it is not knob & tube it should not be a problem for the future sale of the house.
I re-did my previous house about 5 years ago. The house had been built in 1865 so the house had to be initially wired much later. I was generally able to figure out how it was done and routed my wires in a similar manner. Most of the horizontal wiring was behind the baseboards so I didn't have to open up the walls. Generally speaking, rewire the first floor from the basement and the second floor from the attic where possible. It is a lot easier to run excess wire than to open up the walls.