Have you been doing anything specific for link development or have you been focusing only on content development?

In my opinion they need to go hand in hand.

I've been mostly writing articles (thinking that "You build and they will come"). But they don't come as expected. I know how to do link building etc. but writing is so time consuming that I don't have much time for link building (again - probably naively - thinking that both search engines and users will reward the content somehow, somewhere, sometime)..

My competitors work on their online reputation and link building only. But I thought my approach would 'win' in the long term (because - in theory - others should link to my website which has "great content.") Now I feel I'm a sucker or a geek who - instead of 'socializing', making friends, and having fun - was diligently studying and doing assigned homework only to find out the easy approach is more rewarding..

They will come... but only if there's enough fanfare and whoopie that brings them there. It is one thing to know about writing; it is another if you are writing the same thing over and over. If your niche is narrow how many ways can you describe really big red widgets? Sometimes 10 pages are better than 100.

Pick and choose your battles. Never assume you have "great content"... the web is a fickle and sometimes stupid zone. By the same token, don't produce #s*t and expect a landslide of visitors. Ain't gonna happen. Avoid the sucker moniker by doing what you like best, can do best, and EXPECT NOTHING FOR HAVING DONE IT (yeah, I know that's a shout!). There is no "easy way" to get 'er done. There is only that nifty keen combo of content/keywords that attracts the SEs to put your particular content high enough in the serps to hopefully generate visitors.

Meanwhile, write good content!

I agree with Fargo1999. For a new site a "quality content" strategy won't work. Spammy link building, by contrast, will work.

thinking that "You build and they will come"

They will only come if they know about it.

Quality content must -- repeat MUST -- be backed up by some form of active promotion, otherwise not much will happen.

My recommendation would be to shift your focus for a while to invest some energy into quality link building and general promotion.

You've worked to make your site good, now do some work to make it known.

Its the link paradox. Great content brings links, but only if the website is in a position where it can develop enough traffic to consistently see that content.

This is one reason why I wish Google would provide a longer leeway term for new websites in the index, since they would then have more time to prove themselves.

Your content might not be as interesting as you think it is.

I'll spend hours researching, writing and polishing an article, only to see it wither and die from inattention; while a simple embed of a goofy YouTube video gets hundreds of link ins, retweets, Diggs, Stumbles and Facebook links.

my website has 400+ well-researched and useful content pages

Then if someone searches for phrases found in your documents, you will come up at the top of the SERPs especially if your content is original, even if you have no external links. Now perhaps the content of pages is not as useful as you may think and that is subject to what people search for.

If you try to capitalize on a popular phrase where many bid for, by posting new content, you will also need references. But to detriment the site's content in exchange for spending time posting spamy links in social sites, isn't good for business.

Be careful on GREAT useful well researched content.

• Great content will bring you traffic, yes, for sure
  
• Be aware that too much effort will make your valuable work "a great resource page" so, as one project I have, people come for references (researching, studying) and that's another kind of traffic that perhaps you won't find useful because they come, read, copy and leave.
  
• GET EXPOSURE, trusted links. Lazy webmasters might find your site and use if to copy & paste... Some complain as other sites get spidered first than the source, so beware of this, make clear you are the source.
  
• Great content needs exposure so people get to know your site
  
• Analyze your website, info and audience. Some (as you mention, via PR) only want things to do, see and visit, instead of reading research.
  
• Per example, I have a great website about "the land of widgets and how to build them", great info but the audience is more interested on VISITING the land of widgets and a tour around the factory of widgets than reading about it.
  

Remember, you can have little, lots of traffic and also high or low traffic quality. You could focus on little but high quality traffic in the meantime, while the final goal is lots of high quality traffic.

What I mean is I have competitors with 3X the traffic but they make less money.

I do not want to sound harsh but are you sure your content is 'quality' content? You might be missing something to not do well with 400 pages of useful content.

Check out your referrals. How many visitors are you getting from search engines and for which keywords? You may want to review if your site has basic SEO elements in place. Sometimes changing a few things here and there can bring about massive changes in SERP position and traffic volume.

Useful content is more important these day but good backlink buliding is also more impotant.