I've tried to go to Yosemite 4-6 times per year every year since 1985 and I've never had a problem. I have heard that there is some theft at the popular parking spots like Glacier Point, but only if you leave expensive valuables visible in your car. If you take the normal precautions. put things in your trunk, I think it is pretty safe.
The only problem I really see - and I don't know if it is a "crime" as much as a violation - but we live in a country where pets are now treated as children. Each year I see more and more people ignore the prohibition of dogs on the unpaved hiking trails. Most trailheads have a sign that can't be missed prohibiting pets on the trails. But people more and more ignore them. When I POLITELY mention that park rules prohibit pets on the trails, I have minimally been ignored and in one case threatened. These people are NUTS and nothing you can say will change their mind. I have NEVER had one person turn around on the John Muir Trail if they had a dog with them. They know there are no park rangers around, so they just do whatever they want.
If I was the park superintendent, I would start posting LARGE signs noting a $500 NO EXCEPTION fine for anyone that violates the rule. Until people start seeing the park take action, this problem will only get worse.
Hey, I LOVE animals. I am one. But if we only obey the rules that we like, chaos pretty much is guaranteed. If a person can take a dog to Nevada Falls, why can't I saw down a few trees for a nice campfire?
I blame the Park Service. When they don't enforce the law, why would anyone care about violating it? When I mention the problem to Park Rangers, they just shrug their shoulders. I'd like to know if they ever actually enforce the law and fine a person. I'm guessing they don't.
Okay, I'll get off the soapbox.
Bill