..You did not tell me about the "ground down lifters". That is a whole different issue and is part of all of the cam and lifter issues going on right now. That should never happen. You have a cam and lifter problem. That is whatt he original cam problem was like in the type 4's. Constantly changing valve gap...and the loss of about .025-.040" of metal in 30k miles on the lifter faces. Its days are seriously numbered. I thought your gap sounded excessive. But generally....when you are not on the base circle and you have a high lift early closing cam....you can get up to .030" or more...gap.Its not really true that the valves wear .0005 in 500 miles....or at least they should not. Its not normal for modern material valves to stretch that much. That means that every 3000 miles, your valves will essentially be in contact with the adjusting screw cosnatntly at TDC...when warmed up....if that were true. This is due to the fact that you normally have between .002 to .004 gap when hot. You should not be having to adjust more than a couple valves more than a thousandth or so, every 3000-5000 miles. A lot of the variation seen, also has to do with variations in rotation of lifter and pushrod on the face of the cam...and the difficulty of actully getting the cam to the same exact TDC each time, considering that it is not actually on the base circle. It still on a ramp.
One of the reasons setting the valves with less extraneous slack in them gets you more and better life on your valve adjuster screws, is that there is less pounding on them.