Broadly speaking, there are four basic ways you can get hurt with a gun: a premeditated crime, a crime of passion, an accident, and suicide.
Premeditated crimes, understandably, aren't deterred much by bans or checks. Someone who's already made a conscious decision to be a mugger or a gang hitter or whatever doesn't care, and black-market guns are readily available for people willing to associate with, well, black-market gun runners.
Crimes of passion, on the other hand, respond very strongly to whether guns are available or not. This makes sense: if you're pissed the hell off at Joe, and you have a gun, you might very well shoot Joe (with or without thinking of the consequences). On the other hand, if you have no gun, you're not going to go out and wait a week, or mingle with a criminal trying to get one, you'll just punch him. (Or stab him, or try to run him over with your car, but that's as may be.)
Gun accidents are more or less strictly reliant on the number of guns, just like every other kind of accident. It's true that, statistically, the only way to completely prevent gun accidents is to completely prevent guns; on the other hand, that doesn't stop us from having and using all sorts of other dangerous things, and there are well-reasoned precautions that drastically reduce your odds.
Finally, there's suicide. (I heard during the election that gun suicides outnumber gun homicides in the US by something like four to one.) A waiting period can make a huge different here; suicidal ideation is surprisingly ephemeral. A person can go from wanting to jump off a bridge one day to completely baffled why they would do that the next. (An aside: gun suicides aren't as foolproof as people think. Whether that's good or bad depends on your opinion on living with horrible, crippling brain damage as a result of missing.)
So basically: are waiting periods and other methods of restriction foolproof? Of course not. Are they valuable? Certainly; strongly so in some cases, weakly in others. Would they be more valuable if they were more restrictive? That, I can't say with any certainty. My instinct is "probably not that much".