The "+3" goes with saying that if you live in a densely populated area, esp. in an apartment complex, you are at much higher risk. That said, you really need to make sure that no one is "accidentally" accessing your network--THAT happens millions of more times than actual illegitimate hacking of wireless networks does. I like to ensure that my neighbors are not unknowingly hogging my bandwidth. I know they all pay the same ISP that I do, so there is no reason for them to do so. Besides, they are all novices anyway. LOL
I use MAC filtering. Only 5 PC's and one phone are allowed to access my network. Other than that I utilize all of Linksys's firewall and encryption options with the exception being WPA2, which appears to be a lost cause anyway if some wardriver actually wants to risk his personal safety by parking in my neighborhood to breach any given router. Everyone is armed to the teeth here.
I also have an ATF agent, an FBI agent, a State Trooper, and two other law enforcement officials for neighbors. The rest are war vets itching for someone to mess with 'em. Then there are some Ulster Scots too. We know about them. LOL