The 250 exhaust was mild steel from the factory as opposed to stainless steel,admittedly very heavy gauge and this accounts for the very quite nature of the car, a SS system would allow a lot more noise to escape as it would be made with a far thinner gauge material, That exhaust looks very much in the same condition as mine and unless its actually leaking anywhere then it should not be a worry, yes it will go eventually because it will rust and the favourite site is near the crutch of the 'Y' section, but it may just look a lot worst than you think.
Also could be a possible bargaining point!