I am wondering what your opinions are do you think that all the 4 character domains will be a wise investment or do you think they will never be worth more then the 10$ you pay for it.

I think it depends more on the specif characters in the name. If they spell out something meaningful and memorable then yes they're probably worth a lot. They're also probably taken. If you're talking about random strings of four characters then I'm not so sure.

Some probably will be others probably won't be.

These 4 letters can be worth much or not. All depends on these letters.

Four letter domains will always be a wise investment if it has some meaning or a word in it. It can also be a keyword someone is targeting for. There are very minor chances to get such domains nowadays as they are already taken by someone and even if they are available with the registrars the prices quoted are very high. If you get any for investment purpose it will be a good one I must say.