I've turned most of these off. The weather is useful as is commute information, but site updates and things Google think I might like based on my searches are generally poor. There was a recent reminder not to forget to vote and occasional "are you interested in such-and-such an popular event" cards, but these never seem to have an option to prevent recurrences.
Parking information would be useful if it were both accurate (it isn't, due to taking a park and ride bus) and consistent. Like many Google Now cards it seems difficult to predict whether it will turn up or not.
Another trick it used to do was show me cards with navigation information to somewhere I'd searched for, usually the night before a trip. But, when I got into my car at 6am the next day such information was nowhere to be seen and I'd have to search for it again. Now I save the location in the calendar so at least there's a link to click, causing Google Now to remind me to leave on time after I've already left, sometimes when I'm nearly there.
Overall, it's not a useful product and relies upon data being collected which I'd rather wasn't. The only reason I leave it on is so that I can dictate reminders to my watch, which I find a very useful feature. The requirement to use Google Now for this last feature seems rather arbitrary to me.