SEO-lesson: Should I Change My URL?

Yesterday, I just came across an article talking about optimizing onpage factors. One of the factors the article mentioned about is the way naming your URL. When I created my site 2 months ago, for consistence, i used all underscores for my subpages; for example, for my platform bed store page, i named it bestplatformbeds.com/platform_bed_store.php But according to that article, hypen is better than underscore becasue most search engines treat hypen as space, so to search engine, a hypen will be like "platform bed store". Unless you are targeting the keyword "platform_bed_store" then it is better to use underscore in your url.
Just when I want to change my URL and use 301 redirect for my pages, I got some other advice from the forum that changing URLs should only, only, only be done for a really, really, really good reason and in my case it will be like SEO suicide. URL has a minimum effect on your ranking, if any at all! Just want to share with whoever considering change the URL without a very very very good reason.