Personally, if it's running well, was serviced a year ago (filters, oil, plugs) and has only done 3000 miles, I'd just ride it.
Ask the MOT guy to advise on the general condition of the brakes, suspension, chain/sprockets, wheel/steering bearings, etc and spend your money where he advises (if he seems legit and) if you want to.
Servicing yourself is all pretty straight forward. The fazer is well built and as long as you keep on top of the oil/filter change interval, it'll just run and run.