I cant help much but with my experience with reliquary tower, three factors need to be in effect.
-are you drawing a lot of cards?
-are you wanting the large hand to have options?
-how many cards can you play on your (or any) turn?
My dragon deck does run reliquary tower, but it draws a lot. I like having options and i can get to the point where i am playing five or more dragons a turn.
I think I only ever have Reliquary Tower in one deck. Xenagod wants it because when you draw 12+ cards at a time, you still want to reliably hit those land drops and chain that efficient ramp to enable consistent pressure or threaten one-shot kills.
Scavenger Grounds is one of the best colorless lands printed in recent history. Though if you've graveyard packages it's difficult to include in. It's perfect for linear strategies that don't wanna miss a beat.
There're more options than just these lands.
I normally don't go over 9-10 colorless lands in a mono deck, much less for 3C and above.