Good spelling is a sign of attention to detail-- doesn't have a lot to do with formal education or even i.q. It's a sign of caring about the correctness and precision of small things even when the consequences of messing up are trivial and most people either won't notice or won't even know that you messed up.
For instance, saying "your" all the time when you mean "you're" is just plain laziness and carelessness.
I understand what you mean and my precision-bordering-on-OCDness must be on constant guard not to overemphasize spelling and grammar. It helps to remember language is a living organism, with rules that are often arbitrary and change over time, and sometimes for bizarre reasons.
If you speak and read more than one language it's tempting to cling to rules as to a liferaft, but again, it's a losing battle. The rules will change on you, especially the pretty, complicated ones that only you know. And then someone will publish a new dictionary saying that the rules have been changed because, after all, they are continually broken in "common speech". Been there, done that, totally have the tee.
Fitzgerald's spelling was supposedly atrocious. He had an editor.
