I think draws that are agreed to should not be allowed, period. The only allowed draws should be where it could be shown that neither side can win, like insufficient force, perpetual check, repeated positions, or by stating one's line of play and the tournament director agreeing to it being a draw. Agreed to draws just make it easy for both players and allow shenanigans to happen in tournaments by letting some players advance to the next round without having to really play some games.
Yeah, I've heard the bit about they'd be wasting their time by playing it out, but I sure don't see the point in playing if you're not even going to play the game in the first place.

Making this simple change would certainly lower the number of draws in Chess that I hear people complaining about all the time, and it wouldn't change Chess in any of the ways as I've seen some other ideas for changing the draw rules would.