There are 3 reasons why you should spend time on the internal link structure of your site. It ensures that the spiders can find all your pages and index them. It builds the relevance between a page and a keyword. And as a site owner you can determine the PR value of your pages.
Indexing of your website
Ensure that all your pages, or at least those that are important to you, can easily be found by the spiders. This seems logical but if they are not found, you can not expect that one day your site ranks in the top 10. Miracles happen... but not in the SEO world.
More pages means a larger site, allowing you to be seen as an "authority", at least if you have something useful to say. More pages means you can build links between pages. These will get stronger and finally you will build more PR. And the more pages, the more keywords / phrases / long tail keywords you can target and the more pages you will see pop up in the results.
Building relevance between keywords and pages
Before you begin with your internal link strategy you must know for what keyword you want to rank a certain page in the search engines. Your main page will always have your main keywords and your internal pages can concentrate on less competitive keywords or long tails.
The key here is a good anchor text ... If you want to refer to a page that is about the "opening of a shop" and that is the key phrase you want to be found in Google, then use those keywords in the text that lets you link to that given page. Don't link with a text like "in a previous article".
Also try to link from relevant pages that have something to do or might be connected with the opening of a shop. That way you get relevant pages linking to each other.
The green bar
About this (too) much-discussed green poison, I will only mention that you should not be mislead by it however it is still very important for good results. The principle is very simple, the more pages you have, the more PageRank you can get and the more you can divide or send PageRank to important pages in your site. There's a big difference if your site contains only 50 pages of which 10 have PR, or you have a site with 500 pages of which 300 are green.
Finally, I would say, create a good balance between your external link building campaigns and your internal link structure. Create a clear plan of keywords / phrases that you want high scores for in the search engines and try to give the feeder pages good external links.
Do you have any kind of web presence? Do you have a website or a blog? Do you have a Squidoo lens? Or a HubPage?
Then you have something to tell people, right? Perhaps you have something to sell and you want as many people as possible to find your site.