How much corrosion is too much?

I searched the archives, and found discussion on problems that corrosion has
caused, but haven't found any dealing with the role of corrosion in the sale
of an airplane.

I know most of you steadfastly maintain that ANY corrosion is bad. But, in
reality, how many of you have purchased anyway, knowing that some corrosion
existed?

I'm not talking about just the thin white dusting type corrosion that is
almost common in all aircraft. I'm talking stuff where you can see "piles"
1/32th of an inch or so of powder fairly well distributed. I'm not talking
exfoliation type stuff.

See some pics below. The first is an inspection cover. The 2nd is the
interior of the tail inspection area. With mirrors, you can see the "piles"
on the lower surface of the horizontal stab skin.

http://f2.pg.photos.yahoo.com/ph/cor...bum?.dir=/4be0

So, if you're in a dry area, and if you start treating with Corrosion-X or
other, would you do it? The A&P says that it could last another 15-20 years.
BUT... I have to look at resale down the line.

Thanks for any opinions;
Carl