It's late so I just quickly glanced over the posts.
Plug pics are always hard to trust. They look a bit lean to me too. Not sure what the first (#1?) is saying but it's darker. I see some uneven colors.
The bike is stock so be CERTAIN you re-install the factory jetting before doing anything else, unless you live in an elevation that would warrant a change. Stock pilots, air jets, mains, needle position, etc.
Then, be sure the bike is in basic tune. It's some work but it should be done. Check compression, valve clearances, solid/clean electrical connections throughout, battery voltage, ignition timing, vacuum tool synch, clean carbs with float levels verified, no intake leaks, good fuel flow and gas tank venting. If you pass on checking ANYTHING above, it may cost you more time in the long run. Older bikes need a complete maintenance check first before any testing. If you feel the voltage or spark quality is poor/incorrect, then there are several posts at this site to help you test for this.
The most important thing I see in your posts is the jetting isn't stock.
The other thing is if you want to test the plugs for correct mixtures, you need to test/chop off and read the plugs correctly. Full throttle for the mains, 1/3 to 1/2 for the jet needles and minimal throttle (under 1/5) works for the pilot circuit. Each jetting circuit regulates a different throttle position range so you must test accordingly.
Plug pics are always hard to trust. They look a bit lean to me too. Not sure what the first (#1?) is saying but it's darker. I see some uneven colors.
The bike is stock so be CERTAIN you re-install the factory jetting before doing anything else, unless you live in an elevation that would warrant a change. Stock pilots, air jets, mains, needle position, etc.
Then, be sure the bike is in basic tune. It's some work but it should be done. Check compression, valve clearances, solid/clean electrical connections throughout, battery voltage, ignition timing, vacuum tool synch, clean carbs with float levels verified, no intake leaks, good fuel flow and gas tank venting. If you pass on checking ANYTHING above, it may cost you more time in the long run. Older bikes need a complete maintenance check first before any testing. If you feel the voltage or spark quality is poor/incorrect, then there are several posts at this site to help you test for this.
The most important thing I see in your posts is the jetting isn't stock.
The other thing is if you want to test the plugs for correct mixtures, you need to test/chop off and read the plugs correctly. Full throttle for the mains, 1/3 to 1/2 for the jet needles and minimal throttle (under 1/5) works for the pilot circuit. Each jetting circuit regulates a different throttle position range so you must test accordingly.
. Did the WD40 spray check for air leaks and didn't pick anything up. I have just sorted the fuel flow. Have checked the tank venting by removing cap and also switching petcock to prime with no discernible change in performance, so I'm assuming that the tank venting is ok??. Will order jets when I find a supplier... (I daren't support the local Suzuki dealer they have no interest in bikes over 10 years old, won't work on them, are as helpful as a boil on a roid and seem to charge 2 to 4 times the value of a fair price). 
You're already a "nice GS guy" I would (hassle factor aside) prefer to do as much of the work as I can, so 'yes' I would appreciate the loan of the tools. Where do I go to find a suitable selection of shims?
