I guess I will chime in here;

It all starts with the SEO Basics (site structure and content). If you do not have a strong foundation to build upon, it will crumble (quickly). You can get 100,000 links, but if your site is not relevant, usefull or user friendly, they mean nothing but waisted time and money. Don't flood your site with modules, bouncy things, etc.. Keep it simple, relevant and useful for visitors. Sneak a little eye candy in there :) (on home page)

Here are the basics;

1- see more Content is KING!
Using Original, Relevant content throughout your site is one of the strongest (longgevity) optimization methods available. When I say "content" I mean, on site content (home page, blogs, forums, articles, extra pages, etc..), Page Titles and Descriptions (*Important*) and Inner Page Links. Having great original content will attract search engines and will be very helpful in getting do-follow links from other sites when requesting.
Of course page url's, domain name, domain name registration length, etc.. help but to start, content is king. .

2- Structure of Site-
Make your site user friendly, different and easy to navigate. You can promote your site all day long but if users come and quickly go, you are gaining unique visitors BUT destroying your individule/overall time on site and bounce rate (never mind retaining any members) . If a users find your site searching for "Tango Dancing" and click through only to click away quickly, search engines (this day and age) look at this as either irrelevant or not preffered to search term. What this does (after awhile) is lower your positioning and relevance score for any giving keyword or search term.
Make sure your site is somewhat different (or offers something different then others like it) and display that on the home page for visitors to see, to retain new member registrations.
Make sure you have a good sitemap, no dead pages (old links or pages), 404 error page with link(s) to another page or pages and Link Specific Targeted keywords throughout content to its approporiate pages. As changing the url page structure in dolphin could be a big pain, try and keep titles, description and content relevant to each other.
Overall keep your pages clean and not to busy.

3- Link Building & Social Media Marketing-
Link building is of course a real valuable way to gain positioning and become a trusted relevant site. Link building done the proper way (relevant authority sites (the sites that did all of this work already or just have it :) ) will dramatically help your positioning and overall optimization. Getting links from 3 or 4 reputable authority sites is far far better then getting 100 links from unknown sites. Don't just go out and get links everywhere.. Do a little research and go for better relevant sites even though it might take alot more time and work. Having great content and a useful site will make getting these links alot easier. Do not use any paid link service, grey/blackhat method or garbage .edu profile/forum/blog links. Might help a little in begining but will all crumble in short time.

4- Local - Targeted - Free- Who are you targetting?
If your targeting local to certain areas, change your page titles, description, content, etc.. to include local area keywords. You will rank alot better for local targeted keywords (long tail keywords) then you would generic or main keywords. Do a little research and you will find long tail keywords (with local city) will be alot easier to target then national or generic keywords.
There are many Free ways to avertise your business and gain a few easy quick links. To start of course setup Google Places, Yahoo and Bing (have a friend or two give you a review or 2 a week later lol). Also, enter/submit your site to review websites and bigger directory sites.
Another way we have found help alot of sites (not free, unless some business sponsores) is to give away something. We found (contests) giving away a $30 -$300 item from time to time will help get new members quickly and also hopefully get another site or two to link to your site for the giveaway (be creative). Market this to all social media networks (if local, market to other local websites). Make sure your site is user friendly and useful, otherwise you will have 1000 members but no active members as they just wanted the giveaway.

5- -Social Media Marketing-
As we all know, this world has turned into a FB frenzy. Capitalize on the fact that people are addicted to Facebook, Twitter, etc.. by marketing a give away, contest, free membership, classes, a car, etc. you will not only attract your FB friends on your list, but others will follow if done in an effective manner. The easiest way to promote or get the word out this day in age is Social Media. Everbody wants something for basically nothing, it's just human nature.

6- The Truth-
I know you do not want to hear this but, if you have tried all of the above and more for a period of time with un-satisfactory results and can't retain or get new members, then it's time to look back to square one, Your Site! You can take any site from nothing and get users to come to it one way or another (being creative and using other people/company tools to your advantage), but if visitors do not like the look, see anything different then other sites like it or is not useful for them, you will be spinning your wheels for a long time. Re-evaluate your site, niche market, site look, targeted prospects, targeted areas and marketing..

There's much much more then 1-5 in regards to seo, link building, marketing, etc.. but if you start with the basics and build upon that, you will not regret one second of it.. Don't just think building links will get you anywhere, it won't, we try many many different variables constantly and always see sites with proper structure and content outlive and rank far better then others without proper structure.

Suggestions for Dolphin-
- Give availabilty for titles and description for each page (there is a good mod in market to build upon, Deano's)
- IMG alt tags
- A social feed for videos, photos, blogs, etc.. - a simple link to share a post, video, etc.. to social networks (facebook, twitter, linkedin,etc.) would help in regards to distribution.
Share a link with proper titles and such will help in regards to site traffic, user interest and browsing. It's all about being social (stalking) these days...

Dolphin is SE friendly and can be alot better with a few minor touches.. Read some blogs/forums and see what the current trends are. BUT it's all about your Niche market..

Good Luck...