Yes, for organic outreach, that's a must. But you need to focus on the areas that matter. Seo is a constant battle, you don't stay at the top just to get there and then do nothing. They stay on top because they have big budgets and teams, but that doesn't mean it's impossible.
Something that a lot of people who do that don't seem to understand. If you're just starting out, I'd recommend reading and doing the SEO yourself. The reason is that the cost-benefit of SEO is rather gradual. Unless it's a really extreme case, you probably won't see your money back from hiring an SEO expert for many months, maybe longer.
It's also useful, if you're a solo site owner, to understand the principles behind it so that you can better manage an SEO expert in the future when you can afford it. This will also give you a better appreciation of the limits of SEO. In short, yes, it's worth hiring a professional SEO specialist. The problem is that it's incredibly difficult to get around all the noise to find someone who really knows what they're doing.
Yes, SEO pays off for a web design agency. If any type of web agency wants to do SEO for their agency or wants to provide SEO services, then they can do it. SEO can be a valuable investment if you're looking to increase website traffic and generate more leads. Honestly, most capable and reputable SEOs who can call themselves experts can easily make money using what they know about marketing and SEO.
It's hard to condense everything I know about SEO into a single reddit comment, but I tried to get the gist of it. I'm curious because my general advice to clients is to avoid spending money on SEO services until they have some form of traction with their project, but if your case is different, it would be very useful for me to learn about your experience and how I could improve my services. Since you have no idea what you're doing, you think that as you start to rank higher, that's what your SEO expert does. If you keep these things in mind, you should be able to find an SEO company worth investing in.
Guys who are TOTAL BOSSES in SEO are making millions of dollars doing SEO on their own sites, selling supplements or affiliate offers or whatever. In SEO for a company, that would mean knowing what SERPs are, how Google Places will fit into your business (if at all), how social media can work with your business, etc. You may need to deepen their knowledge, what their SEO action plan looks like, and the previous projects they did for other clients. Of course, some will say that the moment you stop paying for paid traffic, it runs out, but in my experience, the moment I stop investing in SEO, it's also lost.
I'm in the United States if you need an independent SEO Guy, 10 years of experience and worked full time for the big players before. I have a new site that needs SEO in a big way, and from a point of view of things, it will take a lot of time and effort if I do everything myself. Ultimately, whether or not to invest in SEO depends on your specific needs and objectives as a web design agency. Depending on the agency you hire, you'll have a lot of SEO experts at your fingertips, you can let them know what your plans are for your business.
Now, all that said, I know a lot of design firms that have never done any seo on their sites.