It seems to me that right now, everyone is riding the back of a "social media" source of one type or another, be it Facebook, Twitter, or any number of various sources out there. But let's face it - if you have a presence there and don't regard it as important, you're wasting your time.
Every single part of your company is its public image. Like it or not, your Facebook page may be the only way part of your clientele knows you, relates to you, and interacts with you. If you do a bad job of keeping it up, they make assumptions about your business in a negative way all because of your lack of maintenance. It would be the same if you let your web site go to pot as well.
Face it, assumptions, right or wrong, are made every day about every single thing we interact with. We as humans don't have enough time to connect all the dots or do all the research. So you have to constantly put your best foot forward. Your first impression may be your only impression. So make sure you keep things as timely as you can and update everything you're involved with!
On the other hand, I'm going to advocate something very few people would dare suggest: If you don't have time for social media - DON'T DO IT. It is better to be absent from it entirely than to present a bad image or product. Yes, you must have a web site in today's market. But do you need a page on every other site? Probably not. Would I recommend having one and maintaining it? Yes. But if you can't do it properly, and keep it up to date, it's harming you far more than it helps.
Quite possibly my only exception to the lack of updating rule would be if your sole goal is to have yet another portal for your pricing structures and pertinent information. But at that point you're basically doubling your web page. Social media is not static, and if you don't change your content your page will get ignored. Again, if you can't maintain, I'd skip it.
Because of the growing reach of social media, we're going to hit a time where these things seem compulsory, if they don't already. But keep in mind that MySpace was THE place to be just a year or two ago, and then Facebook exploded. What's next? You can guess, but the best advice is to follow trends quickly and to the best of your ability. You can be ahead of the curve, but in this case, sometimes keeping up with it can be pretty tough. Make sure you can dedicate the time, care, and patience to this that you would any aspect of your business - after all, this is customer interaction in a one-on-one situation. Remember that, even if it's not eye-to-eye.