I would say doing a straight upgrade is perfectly fine, but I also have a MacBook Pro as a backup, so it's fairly easy to throw caution to the wind.
I ran the Yosemite betas and on my main Mac and just updated to the final shipping version when it was available. I had zero problems. With El Capitan, I also installed it over my existing install on my iMac. Until the Beta 5 version, it was a real mess. But it's running smooth now, and I'll be installing the final El Capitan version when it's available without wiping the drive and starting over.
There was a time in the past when I wouldn't consider a major upgrade without doing a clean install. Now, I just keep the installation of frivolous software to a minimum to avoid problems.