If you believe in the long tail theory, adding up SERP results from all of the smaller search engine results can be just as important as trying to score well in the almighty google. So where do you focus your energy? I vote both. At least submit your site to a few of the relevant ones and of course check your keyword density for SEO primary keywords.
Rather than repeat the work of others – this site lists several alternative search engines you can start with:
http://www.hongkiat.com/blog/100-alternative-search-engines-you-should-know/
Yes, many of these search engines are small and hyper-regional, but that matters to the Tendenci community given the open source translation efforts going on at Transifex for Tendenci – the Open Source AMS. We thought it might help you too!