Actually, many people really do their own taxes using various tax preparation programs. There is no harm in doing your taxes so long as you know what you are doing and there are no complications as such.
Whenever your tax return is complicated and you are unfamiliar with a particular item of deduction, you should generally consult with a professional. In this instance the level of income does not come in play.
You could have a substantial W-2 income and no other deductions and you would really have a very straight forward tax return, that you can easily file yourself.
Whereas, in NJ, there are numerous examples where commuters have to file multi-state tax returns and these returns require prepares to have substantial knowledge of both NJ and NY state income tax laws. These returns generally, you should let professionals to prepare.
There may be instances where judgement is involved and only a CPA may be the most competent person to file the tax returns and doing your own tax return may not be possible or practical!