Having been a partner in both a very big law firm and now a smaller, and far less expensive, virtual law firm, and having spent the past 15 years in business roles with early stage companies, I can attest that few companies need the big, expensive firm. I agree that for specific documents like those listed above that professional investors care about, having standardized forms from someone like Wilson makes sense. Beyond that, I would not use an expensive firm for other work. There should be plenty of much more economical options, including virtual firms.
At the other end of the scale, generally avoid solo practitioners who do not have decades of experience. While they tend to be less expensive, they do not have the broad range of experience to adequately represent a company in all areas of law.
Here is a blog I wrote about things to keep in mind to help control your legal expenses. http://www.advocateslg.com/blog/2013/01/controlling_your_business_legal_expenses/