This is a very general question, and deserves a very general answer. (Which is cool.)
You should put as much detail as you need! There's no right answer. In general, stick to the minimum required to move forward. Don't waste your time! Try putting half as much detail in and see if it gets the results you need. You may find that you were wasting a lot more time than you think.
To answer your question a bit more, we need to get back to why we're making wireframes / prototypes in the first place: to test things out. If you're just testing out the IA for your site, you probably don't need to spend time adjusting color schemes or edge beveling. But, if you're testing out a radical new visual design, then you may need to put in the time working on those details.
I'm using "test" in a very loose sense here. A full clickthrough HTML prototype in a usability lab and a simple doodle on a napkin are both tools used in testing. It's just a matter of what you're testing and how accurate your results will be. The HTML protoype will give you pretty accurate information about what users will do with something, but it will take a long time to make. Showing someone a napkin sketch will take two seconds, but will give you really general information. (Maybe even miss-information.)
These ideas don't just apply to websites -- you can make a simple / complex prototype for a car, building, service, song, PhD thesis, whatever. Anything man-made has any number of conceptual levels at which it can be represented! Check out the amazing book Understanding Comics. It'll change the way you approach the craft of UX.