Carfax can be handy just to get some idea about the car, but ultimately it's always best to see a car in person before a final decision. Knowing how many owners a car has had is really about the most consistent info you get out of it as you can have damage that wasn't reported if it wasn't done by a bodyshop or something. Can be nice for seeing recall data and dealer service records, but if the car is that old I wouldn't expect someone to still be taking it to a dealer.
My car has over 100k miles and would probably scare most people off if I tried to sell it and they looked at the Carfax. No service records for the past 60k miles or more, but I change the oil and most other fluids fairly regularly and try to keep on top of maintenance. When it's nice and clean I'm not even sure you could tell it had that many miles on it and it still runs like the day I bought it.