In a situation where there's some complex tax issue, absolutely, go with the professional, but for most people, the CPA is mainly there to provide peace of mind.
Also, if you make a good faith effort to pay your taxes correctly, the potential legal trouble for getting it wrong is pretty minimal. You'll need to pay the correct amount plus interest and penalties, but "interest and penalties" are pretty light (effectively 14% simple interest on the amount of the underpayment). And since the IRS doesn't usually take more than a couple of months to say, "hey, you screwed up," interest and penalties usually add up to like 3% of your underpayment.
Worst $500 spent in my life.
I just searched the site of the person I used (it's a private family company, not one of those cubicles set up in Walmart) and there's no mention of "CPA" anywhere on their site.
He decided it was time to retire, recommended another accounting firm in my area, and they charged me $750, and all it was was an Intuit frontend where I had to fill everything out myself. I did that one year, then I switched to FreeTaxUSA and was super happy with it.
I probably would go back to an individual CPA if I could find one like the guy I had, but I've been burned by the first CPA and this most recent one. 1/3 isn't a good prior.
For federal income tax, there is also this spreadsheet that is very handy:
If it makes you feel better you can use a CPA once, and then mimic what they did in the years later. The best service they can do is recommend things that may minimize tax or reduce complexity. Note that minimizing tax may not be the best goal, however, especially with investments.
Or you can pay a CPA to do your taxes to feel like a "big boy".
Different story if you're self-employed, own a business, or are involved in various types of investments.