I dont think this is very good advice. I know plenty of people that took a year off to do research because they wanted to match in a competitive field and said that it considerably improved their application. They had presentations at meetings, some had publications from that year, and all said they developed relationships with people in their desired field that led to strong letters of rec for their application.
That being said you have to have a reason to do it other than, "I did it to be more competitive." And if you don't know what you want to do, then it's hard to target people to do research with for the purpose of getting good letters. You have to have some interest in doing research going forward to make it truly worthwhile.
But, there are certainly people who become more competitive by doing a year of research you just need to have a bit more of a plan than it seems that you currently have. For example, I want to be more competitive for a plastics residency so I'm going to work with Dr X (chair of plastics at your med school) with the plan to make good connections for letters and get a few presentations/publications on your resume.
Good luck, but dont just go get an MPH so that you can put 3 more letters on your white coat, that sounds ridiculous.