As already mentioned, if you're going to drown your bike via holes drilled in the airbox lid, you're likely going to drown it without the holes. Doan worry 'bout it.
'Good 'ol soapy water' isn't going to work with a decent filter oil (which you should be using...NOT motor oil). I second the 'notoil' comment. Their filter oil is a sticky mess (that's a good thing)...and you're NOT going to get your filter clean with that 'good old soapy water'. Notoil's filter cleaner makes the whole cleaning process a 90 second deal! That's if you're pretty slow about it! Simple.
Heck..you can wash the thing in your clothes washer if you wanna. After your wife finds out, you may wish you had used the sink, though.....;)
re: why drill the lid?
Cuz removing the whole thing allows unwanted detritus inside...and the noise is IRRITATING!! An IMO of course. Some riders like the 'dead duck quacking' noise. I don't!
Do you have to rejet? That's a question of concern. If you have NOT changed the jetting on your bike, you're missing out on the biggest performance BANG for practically no $$. If your jetting is spot on, and THEN you remove your airbox cover OR drill holes in it, you had better rejet, cuz you'll stick it.
If you didn't find info (THANKS for looking, though!) concerning airbox lid mods, I gather you haven't been to CDave's site? You should take a gander...@:
http://justkdx.dirtrider.net
You'll find xlnt starting point jetting info there, too. Lots of just plain 'ol great stuff on CDave's site.
re: compression testing
Too many variables to give you a specific number. Guages, methods leave too much to chance. Where it will help you the most is using it as a 'relative' comparison method. If you have numbers from YOUR bike, taken by YOU one week after your last rebuild...then you can realistically compare that figure to what you have now.
That said...on a warm engine, several kicks @ WOT---120# is on the low side. 140-160# is closer to 'normal'. If you have a couple years on your bike, and you ride it much at all...it's time for a topend. It's more a maintenance issue than 'fix it cuz it's broke' issue.
re: premix.
Maxim lists premix ratio recs for different bikes:
http://www.maximausa.com/
'Size matters' is what it comes down to. The bigger the bike, the more oil is required (for one thing). 40:1 is safe for a 200.
re: spooge ('spit out oil')
You don't fix that by changing your premix ratio (ex: 40:1 to 50:1). That's making the situation WORSE...cuz you're going RICHER on the air/fuel ratio. Spooge isn't an oil issue, it's a jetting issue.
You're on the way to finding all sorts of power you didn't even know your 'lil kawi had.
Have fun!!