Perhaps the wisest approach now is to focus heavily on your onsite optimization (without overdoing it, of course!). You should make sure your pages contain the best, most relevant content possible. Aside from sharing them on Twitter and other similar sites you really shouldn't do much more than that.
Not only will all that top notch work directly result in improved rankings; in time it will also attract natural links, which are of course gold for SEO.
But what if you have, say, a static ten page website, and even after making it close to perfect in this regard the higher rankings take forever to eventuate? This could be extremely frustrating. You could be caught in a real state of inertia, not wanting to tweak your pages any more for fear of losing the search engine traffic they are getting. I suspect there are quite a few webmasters -- particularly ones with small business sites -- who are in this position.
This is why, if you are one of these people, you really must add a blog. Merely updating it regularly will give your website a "pulse" that is a bonus in Google's estimation of its value.
And with each post you publish you have another opportunity to jag some more long tail keyword traffic. Those posts can function as linkbait as well. Since you've already perfected the static pages, those linking to your individual blog posts are more likely to link to some of them, too. So you'll be speeding up the process of natural link accumulation.
Unless you went overboard with the blog, adding hundreds of pages in a short space of time and veering off topic quite a bit, the chances of it negatively impacting your website's SEO are very small indeed. Having all that extra associated content would be overwhelmingly positive.
And apart from anything else, blogging is a proactive activity, which gives you a strong sense of empowerment. That's worthwhile in itself, I believe.