Well I agree absolutely with most of that. 2008 and still on the original plugs? really? Iridium plugs though? I'm not convinced of the case for them unless you're clocking up a lot of miles. I run both our Panda and our boy's Punto - both FIRE engines - on standard "copper" plugs - mainly because our factor sells me standard NGK plugs for "silly" money making it a no brainer. They stay in for 2 years and then get changed. I'd say also that the earth strap needs a good examination and a vigorous "waggle". If lots of green dust comes out and it looks frayed, as they are prone to do, then definitely change it. However I think a poor earth cable will give poor cranking so would have been noticed already. These cables are a known weakness though so worth changing anyway if a few years old.
A good way to eliminate that earth cable is to use one jump lead connected between the engine block and a good chassis earth point. That will "parallel" the earth cable and eliminate it from the equation if it's either internally corroded or is making a poor connection somewhere.
Plugs have a service life in either miles or age, standards ones are generally regarded as in need of replacement at 2 years old Iridium ones at 5 years old unless the car has covered a substantial mileage in less time, Eg. 65,000 in 3 years for iridium say, I'd strongly recommend they are replaced even with standard ones however I would have a garage replace them given you say they've been in 14 years?
I think that's an excellent idea as, if they are the originals, they will be "standard" plugs and quite likely to have corrosion problems after so long which can be a very difficult problem to deal with if you've little experience.
