What is the preferred method for cleaning glass that you do NOT want to damage or scratch in any way?  What about the lens cloths that are made of some Spandex type material?  Are these ok?  Is there any concern about dirt becoming imbedded in these, and scratching the glass?

You should just buy a Trijicon Lenspen, there only like $8.

It depends on how nice/expensive the glass is.  The prefered way for the most expensive stuff (NV/Thermal) is this:

1.  Spray the lens from a glancing angle with a can of compressed air to remove larger pieces of debris.  If you go straight into using a lens cloth, you will inadvertantly rub microscopic particles into the glass coating, scratching it.

2.  Use a soft brush (like the one that comes in a lens pen) to lightly go around the edges to loosen up any debris that is caught in seam between the glass and the housing.  Spray with air again if needed.

3.  Use a lens cloth or lens pen to gently wipe out smudges and finger prints starting in the center and working your way out towards the edges.  Use ting circular motions.

There is this tutorial from US Optics.  Personally, I think it is a bit overkill, but if you really want to be careful, it should work for you.  I just use a lens pen and a lot of compressed air.

www.usoptics.com/video/cln1.wmv

Quoted: I'll add to what CLASKY stated by telling you to get a small magnetic particle camels hair brush to first remove dust and other small particles from the lens.  I have some VERY expensive astronomy scopes that make my NV gear look cheap and this is serious business for me cleaning optics the correct way. Vic

Are you saying that you use the Lenspen for your super expensive glass?  Or a lens cloth (Spandex type material?

microfiber, lenspen and compressed air

If the sight doesn't get hot you could put some cling wrap on it during training and tear it off when done like a nascar windshield or the chinese restraunts do their cash registers.