Depends what you're building. If you're in the medical device industry, it's extremely important. If you're not in some similarly regulated field, the importance goes down a bit. You never want to be using junk, of course.
This is an interesting question, and this issue was raised in the EnginSoft newsletter where the importance of Simulation Quality is needed. http://www.enginsoft.com/newsletter/2010_3/index.html (p.46).