Very interesting. I find the wiggly lines don't appear when I have the Mail Preference window open. When I close it, they come back.
I have had Mavericks since it came out, more or less. I work on the Mac, all day every day, and like you I lost about a fortnight trying to get the thing to behave in a stable way. Eventually, it has settled down, but there are lots of irritations. But really, Mail is dodgy, Safari no longer reads online MIDI files, my five year old Samsung scanner won't work because there is no driver, the new Pages is hopeless, Maps is poor, my iPod is unrecognised by the OS, etc. I like some of the things, but I could live without the notification panel, especially since incoming emails have been known to appear there and then disappear. I bought Microsoft Office because the Apple programs were so feeble and unreliable. I have never liked Word, but it is reasonably reliable these days.
My view is that Mavericks was designed not only to look like a big iPad (that stupid LaunchPad) but also to work mainly as a "hub" for your other devices. That's why the much ballyhooed "never lose a document" thing only works if you want all your stuff in Apple's cloud. I don't. And the Mac apps have been deliberately hobbled so they don't overpower the versions on the iPad. Why did they get rid of Save As? Why did "Library" suddenly become a hidden folder? There are a thousand irritations until you get used to it. Eventually you forget about it, but I agree, I had never had the slightest trouble with an ugrade before and with this one I had nothing but.
They really don't care about the desktop computers any more. No-one uses them except those who use them for work. Cook hasn't got a clue, if you ask me, and Jonny Ive is only interested in fascinating debates about skewomorphism or whatever it's called. But I'm here for life. Windows 8 is OK, but it has all the same problem. Still, I'm very excited about a wearable controller for my iPhone…