It can definitely aid in investigations. If you find someone possessing a stolen gun, then you can immediately convict them of 2 crimes: possession of stolen property and possession of an unregistered firearm. It is a few short steps from there to finding the actual robbers (if the person in possession didn't commit the theft in the first place).
Too bad for the police that they used the registry instead to harass people that did not commit any crimes.
The police should need a warrant to access any sort of database like this. It would maintain its utility, and wouldn't have any impact on citizens.
That would be at least 3 crimes. The person that the rifle is registered to would be charged for unsafe storage and possibly as a result be held liable for for any crimes committed with it. Then again other than poaching there are not many crimes committed with a rifle anyway so there is no point to registering them, especially when they can't even control all the handguns that ARE used on a daily basis to commit crimes and have had registration since the mid 30s.
BTW sniper rifles are prohibited weapons so the NDP amendment would be useless. Like the NDP