We frequently receive contacts from business owners looking to improve their online presence. One specific request we hear is "I don't want/need a new website right now, I just need SEO (Search Engine Optimization)". Each case is investigated individually, but often times, we find ourselves explaining why that probably isn't what they need.
There are two main aspects to a proper SEO campaign. The "on-site" concerns include website structure, naviation, and content, as well as the more esoteric, like server setup and domain canonicalization. "Off-site" aspects include link building and maintenance, proper "local" registrations (Google Places, Bing Business Portal, etc), and social networks.
When a customer comes asking for "just some SEO, not a redesign", they discount a large part of on-site optimizations that can be made. Depending on the current site, the "content" may well be the only thing we as an SEO consultant would have any control over. Given the restrictions existing sites sometime impose, the customer thinks they're asking for SEO, but in reality all they can get is SEO-optimized copywriting assistance. We have talked to people who literally drew a box around the "content" portion of their site and said that is all we could change.
This is essentially fighting an uphill battle against a navigational structure made out of hover-over images, malformed HTML, and www vs non-www (and sometimes raw IP addresses). Any one of these problems alone can be overcome, but time and again we've seen combinations that would make it hard to outrank the competition.
But, can't we still do linkbuilding and registrations? Of course, and those definitely help. But, without the ability to change the navigational or URL structure of the site, links would back to "yoursite.com/post?id=123". A proper redesign of the site would have these page URLs fixed to "yoursite.com/product-name", and while we can "301" a broken link to it's new home, ideally all those carefully procured links across the internet would point to the right place.
All of this hasn't even touched on the aesthetic appearance of the site, or how well a visitor would convert into a lead or customer. It's of little value to rank well for a term, only to have visitors abandon your site quickly.
A properly designed site makes for a much better foundation for any marketing campaign. A few times, when the true goal is to rank highly for specific terms and convert visitors, an old site may be such an unfortunate state that we have declined to do only SEO for the old site without a restructure or redesign. We couldn't in good faith take the job, knowing the likely outcome wouldn't match up with what the customer really wants.