Just for interest (although you'll be the judge of that, of course) there are a number of countries currently recycling P-3 's out of AMARC at Davis-Monthan AFB with completely refurfished and modernized operational equipment, and these are definitley Nimrod vintage airframes, so somebody, somewhere, has done a cost-benefit analysis that shows it can be worth the trouble.
Link to AMARC:
http://www.dm.af.mil/amarc/index.html