I'm in the process of rebuilding a spare engine and I am debating whether or not to fit a new crankshaft or reuse the servicable old one. If I do replace it it would probably make sense to convert to a GP one but then I'd have the added expense of new bearings and seals and flywheel etc and then I might as well convert to electronic ignition and the bill is a lot for a simple crank replacement . its always a case of how long is a piece of string really.
if you replace one thing you need to look at replacing other associated components and pretty soon you've ended up with a completely refurbished engine and a butt clenching bill.