I would rather make the underlined part "non-contributing members". The people who contribute actively (not necessarily with money, but by writing interesting stuff that attracts readers) already help to enhance the value of this resource, and also deserve to have their voices heard. 
Yeh fair enough, difficult thing to isolate perhaps.. only nils would have good stats on the number on non contributors be they guest of member that spend time here.
It also depends on what revenue he gets out of the ads though.. there might be masses of exposure to the forum from silver/guest comparatively to gold, and the forum itself may also produce limit revenue.. the money comes from gold members, who may well remain gold members regardless of the forum because they are here to get the sheet music.
I didn't mean to single out valued silver members such as yourself and suggest you should be targeted with ads and me not as a gold member.. I'm just thinking aloud about the business side of the forum.