There is, and never has been, a "screen protector" for any model of Mac that I'm aware of. Are you thinking of iPhones and iPads? Because there are of course a ton of them available for those products.
As far as cases go, the only reason you should get one for a laptop is if you're looking to customize the appearance of your laptop, as it will do little to "protect" the laptop if you drop it. Further, the value of the laptop is based on its age, and whether or not the screen is cracked or not. A few scuffs and scratches on the case isn't going to affect the value (extreme damage excluded).
Not necessarily.
Unfortunately around November of 2011 my house was broken into. The idiots tried to take my TV, did take my Playstation 2, my Canon Eos Rebel T1i, a few games, and tried to unplug my PC and Linux box to take those (but couldn't figure it out. In our living room we have 4 bookshelves full of books: historical books, kid's books, SciFi/Fantasy books, the lot. None of them were touched. And that was a good thing...
Why? Because both my wife's 2008 15" MBP and my mid-2011 13" MBA were on those shelves hiding in plain sight:
They literally thought they were books, especially since she had dropped $2100 at the time on her MBP and I dropped $1900 on my MBA. When you have the security by obscurity premise of hiding your tech in plain sight, especially when it comes to theft prevention, a case may be your best friend and more than just eye candy. That's why I went with the BookBook by TwelveSouth. They don't have these out yet for the latest Macs, but when they do, I'm guaranteed to get one.
Side note: We didn't get back the camera or the PS2, but that's okay: insurance covered all of it, so we ended up getting the next camera up (Eos Rebel T2i) and the PS3 that had the PS2 backwards compatibility chip in it to play native PS2 games.
BL.