I read up on this because I had a really bad sinus infection a couple months ago and found myself taking "Emergen-C" every morning, which advertises "1000% your daily value of Vitamin C". Immediately after my sinus infection cleared up the virus stuff started, so I kept taking it for a while.
From what I read, at least with Vitamin C, you have to get into the 2000% range before there start being negative side-effects.
The other thing I've always heard is that taking more than the recommended amount is pointless, because your kidneys filter it out. I definitely wouldn't take the time to adjust to an even higher dose. I was mainly only taking the dose I was because I didn't want to try and subdivide the little packets.
From what I read, at least with Vitamin C, you have to get into the 2000% range before there start being negative side-effects.