What is the advantage of having 12mp or higher dslr camera?

I have a d3000 and i'm wanting to upgrade to a better nikon

Being able to make large prints

More megapixels won't change anything. Your question is quite unclear too.

There's a D3100 and d5100 as alternatives below $1000. They are great but quality is the same.

Here's a DSLR Buying Guide - http://www.the-dslr-photographer.com/2009/11/which-dslr-to-buy/

Bragging rights for when you're with your friends.

If you're still in the stage that you think megapixels matter that money for an upgrade would be better spent at a photography course.

The point of having higher megapixels is to create more detailed and clear pictures. However, even if you had a 25 megapixel camera used incorrectly, your pictures still won't be good. Megapixels are very often used to suck people into buying more expensive cameras than they really need. Also, once you get anywhere above 8 megapixels, the less improvement per megapixel. For example, if you have a 5 megapixel and a 6 megapixel camera taking the same picture, there's an obvious improvement. However, if you did the same thing with a 11 and 12 megapixel camera, the effect wouldn't be as noticeable. The bottom line is, it's better to use what you have with nicer lenses and flashes than buy a more expensive camera.

There are really only two reasons. One, to be able to make larger prints. Two, to be able to crop and still retain image quality.

Aside from being able to make larger prints? None. You should already know by now.MP is just picture size.