If you are a small one-person shop, SEO is still a very important investment, but it may make more sense to do SEO on your own than to hire an agency to handle it. To answer the question, yes, SEO is a valuable investment and worthwhile. Aside from the fact that Google likes older domains, big brands have simply been doing SEO longer, so they have more stuff and know what works and what doesn't. We've been saying for months that SEO is getting harder and harder, and that it's especially hard for SMBs to stand out.
In fact, you have to do at least the bare minimum of SEO if you want to have a reasonably viable online presence. If you answered yes, my guess is that you're getting little or no value and you could be hurting your website's ranking if the company handling your SEO is creating spammy links that Google penalizes. When I started the company I had one strategy in mind: build my business using SEO (or search engine optimization). The key ingredients missing from this equation are the likelihood of getting higher search rankings (based on the difficulty of ranking for a keyword) and the time it would take to rank (based on the SEO manager's skill set, strategy, and successful execution of the strategy).
So, in short, getting the right traffic to your website is not only difficult, but hardly measurable using SEO. If they had run a PPC campaign, they would have figured it out within a week and cancelled the supposed SEO campaign, saving themselves thousands of wasted dollars, and lost opportunities. A large company's in-house SEO has tools at their disposal that automate some of the time-consuming tasks in search marketing. The one common metric that all SEO agencies shove in the face of every business owner who hires them is Website Visitors.
An SEO specialist who lives and breathes search has time (and incentive) to follow industry publications and keep up with the rapidly changing search landscape. What's dead are the old SEO techniques that were very effective and could quickly promote your business up the Google rankings ladder, quickly, easily and cheaply.