I disagree. They are not obsolete. They are no longer optimal.
The difficulty of the old and new tests are *roughly* the same. If you have no problem taking the old tests, you will likely have no problem taking the new tests. The main issue is the difference in format. If you want practice the test format, then yes, they are obsolete. If you want to test how well you know the material that will appear, then they are still great resources.
Don't forget, any word/kanji/expression/grammar point that has shown up on any past 1級 test is definitely fair game for them to put on the N1 test, so I'd make sure that you know every single question/answer for the past 1級 tests. You can find some old tests and vocabulary at the following site:
http://www.mlcjapanese.co.jp/MLC_JLPT_Page.htm