You can pick up .info domains really cheap these days. The problem with this however is back in 2006 or 2007 when they first entered the scene they were so cheap that all the spammers headed over to pick one up. For a while, domain registrars were letting you buy a .COM and get a .INFO for free.
It saturated the market with spammers and as a result Google devalued the listing in the search engines.
You'll be hard pressed to find a .INFO domain extension ranking high in Google. It's not to say that they're no good, but they definitely got a bad rap!
You have keep in mind that general public are only used to .com, .net, .org. From a business point, having a .com domain is very important because if your business is xyzcarpets, most users will simply try xyzcarpets.com. If one is simply trying to have a online blog or build an adsense site, they can still manage a good ranking with .info
I agree with you for the most part, except achieving a good SERP rank. Google honestly does not rank .info domains very well.
So if you are purchasing a .info domain with SEO in mind, you'd be wasting your time.