Well in 3.0 there's nothing to stop you placing the sensor, say "five miles directly above me" and getting an aerial view.
As stated, distance is not a factor, and I think the location qualifies as "an obvious one".
Maybe this is what they are trying to prevent.
Snipers
I was not aware that dropping prone is a free action, I though it was a MEA (like standing up). However, your scenario still works with it as a MEA.
However..... Spot and Listen are passive skills. The PCs roll their Spot checks when the sniper fires; they roll their Listens the...
Incidentally, what exactly qualifies a spell as "standard" anyway?
Players don't have to research spells from the PHB, but why does that necessarily extend to the BoEM? What about third party products?
You buy the BoEM and all of a sudden a whole extra bunch of spells suddenly become...
Still talking about tumbling
You may tumble up to 20' "as part of normal movement."
ie. you can move 30' and 20' of it can be tumbling movement which doesn't provoke AoOs. If your max movement is 10' then you can tumble 10' (I guess you could argue that you could only tumble 6.66 feet)...