One of the things that annoys me with PokeVision is that when I scan my house it doesn't pick up my whole neighborhood. Maybe it's because I live on the city line separating Brooklyn and Cleveland but I have to scan my house and then manually scan on just the other side of the Cleveland line to hit the other side of my street (where there is a third rare nest). I definitely have 3 rare nests all within a 5 minute walk of me. One is about 4 houses down the street, the second a bit further about 7 houses down and then the third which is in the other direction and just around the corner. It's the last one that's annoying because it's the furthest away (the 5 minute walk) but doesn't show up on PokeVision when I scan my house.
It also doesn't seem that PokeVision always picks up the rare spawns. I'll have a silhouette on my phone and do a scan for it and come up blank. But since I know the 3 rare spawn locations I'll walk out and hit them and usually find the critter. Knowing how the spawn system works means that I'm catching them more often than not since I just have to hit those 3 locations before the timer runs out. There have been a couple times where I couldn't find it so there is either a 4th spawn nearby or, more likely, the timer is expiring before I get to it.
