Is it worth changing my Nikon D3000 body to D90 body?

Or it is better to look for new lens for Nikon D3000?

Depends on where you want to go. Many people buy the most expensive body they can, but then don't give lenses much of a thought, and often skimp on them. The lens is as important as the body, and in some cases even more important.

Once you have a body that provides good photos, then the best thing to do is to then buy lenses. But one caveat here is that your D3000 will not autofocus many fine lenses that the D90 can, so in some cases, going to the D90 will actually result in less expense for lenses.

Yes, No.
I have a D90 and love it. I can and do use Nikon lenses that are new and AF and great as well as the older non AF Nikkors I have had for over 30 years on it that would be useless on the D3000 body.
That said, if you can wait and see what happens in the next 30 days with Nikon you may find yourself getting the D7000 or a great deal on the D90. Go to nikonusa once a week over the next month and watch what comes out at PMA the big camera show.