Hi Mike,
As has already been stated, this is a very good kabuto and the very fact that it is a quality piece from the Muromachi is quite rare. Some of the damage (such as cracks to the lacquer) can be acceptable depending upon your taste, sensibility and attitude towards conservation and restoration. Many conservative collectors may even choose to leave as is. For me, I agree with Ian - restore/replace the stencilled leathers and fix the haraidate (crest holder) and clean up the urushi. I don't think you have to spend a fortune on it and if you get it for a decent price, it will become even more saleable in the future if you do this work. Ultimately, it's a very nice kabuto from the Sengoku period that any collector would be happy to have in their collection. The menpo is also very nice but in terrible condition and would cost quite a bit to restore fully (and unlike the kabuto, this needs a full restoration - urushi, moustache, new tare). I would treat this almost as a throw-in when you negotiate with the owner.
John