I would stay stock. I have a 78 GS1000 in mint condition on which I sport around and sport tour. I have resisted the impulse to improve/modify because of the effects on metal fatigue etc.. New accessory parts can easily boost performance beyond an older bike's capacity. Eg, even fiddling around with carburetion, sprockets etc can set up vibrations which will wear out cam chains faster etc. Hard rubber seals (such as carb boots) will suddenly spring leaks, leading to overheating etc., If you want to hop up the bike you should only do so on a complete overhaul so that older parts such as bearings, seals, gaskets are not overstressed. When staying stock, it adds versimilitude to keep the stock colours. Best solution, if you can afford is to keep the bike as a local run around show bike and get a newer sport bike for performance.
I now need a new seat cover, and have found that is the hardest stock item to get, and almost impossible to have done by a custom upholstered for a reasonable price - some exotic high tech - heat press is used.