I think you can never have to much rock
But 1-2 pounds per gallon is good. It's a great natural biological filter.
On how much rock is too much? It all depends because some rock is more dense than others, which makes it look like less rock than there actually is and vise versa. It's what you like, visually, because as long as there is sensable room for fish and corals the ammount of rock you add is up to you.
Here is 150 ish lbs of Figi rock in my 120 gal. The tank is actually 41" long because one entire side is an overflow which takes up 7" with plumbing behind it.
http://www.canreef.com/phpBB2/viewtopic.php?t=4210
Steves tank actually looks good with almost 200lbs of rock, I have seen pictures. Maybe do a search on it.