Yeah ... My experience working with Apple with quite a few corporate-owned Macs that have gone in for service over the years? Anything cosmetic is the most difficult to get them to do anything with. On the older aluminum Macbook Pros, the bottom cover used to be really easy to replace if needed. Yet back then, they put such a high cost on the repair part, it made it prohibitive to do as an out-of-pocket repair. And as later models went to this unibody design, it's become a big, labor-intensive job to swap the cover.
Even when you try really hard not to scratch a newer Macbook, I've seen issues where the area to the sides of the keyboard gets discolored slightly over time and looks more like oxidation than dirt you can just clean off. Again, Apple will call this normal wear and tear.
No matter what Apple's advertising copy says about AppleCare+, I'd really consider it more of a way to extend the protections you'd expect from the standard 1 year factory warranty, plus the ability to get accidentally broken screens replaced up to 2 times, if needed. If you view it that way, it's very likely still something you'll want to purchase ... but it's not a magic solution for anything that can go wrong.
Liquid damage is a really tough one because it's ALWAYS been the quickest way to completely destroy a machine. Once you start shorting everything out on the circuit board randomly due to liquid bridging all the connections, you never know what will result. It seems to me with AppleCare+, Apple is more or less saying they'll cover partial failures even if one of their internal sensors changes color to indicate liquid. But they're not going to cover catastrophic failures. Liquid gets a keyboard sticky so some keys stop typing right? Sure, it's covered. Liquid gets in so you see water droplets behind the LCD display but everything still runs? Yeah, they might just give you a new top cover/assembly, dry out the insides, and call it a day. Totally dead and won't boot? Probably out of luck.
