Yeah , well,..as Scott mentioned you still won't be able to put most light fixtures on it ....I still say replace it..
Seriously, I don't understand why you would not want to replace an aged ,inferior product.... seems like the perfect time to do so or at least attempt to do so...
The biggest problem will be finding any enforcable code or law that will require you to replace the wiring, unless there is an out right safety problem, like the house was flooded, I would find it very hard to upsell a total re-wire to a home owner just getting by, and you must present this to the home owner as such, other wise it would be a fraud. Putting a 90? rated fixture in a existing home, would seem to be protected by grandfather laws, not enough has changed in fixture design that makes them more dangerous then what used to be installed, and for that fact there even better, you could pig tail 90? wire onto the old wire to be compliant, or just change the portion of the circuit betwen the switch and outlet, but to wire a whole house, would be a cost most home owners would have a hard time endureing.
Since most newer fixtures will be going to the much cooler CFL's and LED's type lamps, the requirments will or should also go down, the nec is kind of mute on this except for ballasted fixtures where the wires will be within 3" of the ballast (410.33) and the only other requirment as far as the NEC goes is (410.35(A) which requires manufactures who require a higher ratting then 60?C ratting on the branch circuit conductors has to mark the fixture.
there is allot of changes that make some of the older wiring just as safe as todays newer wiring, why is this taking place? well for one to save on green house gases, but it is also taking place because of grandfather laws keeping us from having to bring everything up to todays codes and standards.
For me to go into and try to sell a owner of a house on a total wiring change out, I better have a valid reason for doing so, or I should be held for fraud.
Just think re-wireing every circuit in a typical house avoiding as much disturbing of any surfaces as you can, can cost the home owner as much as $10k-$20k if you think about all the labor.
But just changing out the conductors that are needed can cost under $5k so which do you think they will go for, and which do you think you will provide more safer houses by being able to do more of the jobs? I would pefer to make more houses safer by doing more houses at a much lower cost, then try to make a quick fortune off only one house, which wouldn't be quick anyways lol
