There is no point spending time putting together a fantastic looking website with great functionality if nobody knows about it.
The other thing to bear in mind is that a more search engine friendly site will probably display more targetted adverts if you use contextual advertising as part of your monetisation strategy.
SEO is, therefore, monetisation’s cousin.
Before you launch your new site take a few minutes to check your SEO basics list:

• Page titles – does each page have one? Are the titles descriptive?
• Are the keywords / phrases in the titles?
• Does the site’s HTML validate (or come close to validation)?
• Will it work cross-browser?

The more time you spend on developing organic search the less money you will have to spend on search engine marketing via pay per click networks, such as adwords.