Low reputation users already earn two points per edit once it has been approved.
I don't know what motivates other high reputation users, but I edit loads of questions here and on the electrical engineering stack because the poor grammar and spelling just rubs me wrong - it's like the sound of fingernails grating on a chalkboard. It is doubly irritating on a site about writing - words are an author's tools, but so many make no effort to get things right.
For my part, I'd just like for folks to take the corrections to heart - learn from the corrections and improve the way you write your own answers and questions.
Creativity is one thing - you've got to have it to be an author. Creativity alone won't get you very far, though. If you can't express your ideas, no one will want to read what you have written.
It also takes craftsmanship - you've got to be able to use your tools and materials.
A carpenter with lots of ideas who can't cut a straight line with a saw won't get very far.
The same applies to writing. Your ideas aren't worth much if you haven't got the tools to express them.
As an author, you should always write as though you were writing the most important text ever.
Make it right. Make it polished. Every sentence, every paragraph.
It is all practice for when you are working on your magnum opus. The more you practice, the easier it'll be when you are working on important things.
If you habitually check (and correct) the grammar and spelling of regular stuff, you'll be in a better position to do it when working on the complex ideas you are trying to express in your writing.