And it's the good tenant that calls the city before they sign a lease and makes sure all the paperwork is in order. Of course inspections on registered properties are not perfect, sometimes things fall through the cracks, and some costly repairs are not really necessary. But, as you mention, good landlords are the most likely to register their properties. Those trying to hide something often won't run the risk of having the city waltz in whenever they feel like it for an inspection. Which is why checking your landlord's permits is a low-cost way to get a feel for what you're getting yourself into. If I had multiple cars, I would pay multiple registration fees. If I owned multiple businesses, I would pay multiple business license fees. Tax assessments are a whole different game, since those are based on value, I'm talking about simple registration fees.
Everywhere I have lived, I have seen an inspector once a year. Sure, they don't start tearing up walls, but they check electrical outlets, peek around, and ask if there are any problems. In and out in 5 minutes, but it's nice to know they're there. It's easy to tell if you would be trapped in a room by a fire, it's not so easy to tell how old the wiring is or what kind of current is running through it without someone coming by with that little box once in a while. Would I rather pay $25 or $50 a year in registration fees via rent to know that I have a city inspector popping by on occasion than thousands up front to hire inspectors? Damn straight I would.