Can't stop a downward spiral

My 5+ year old WH site (PR5) is going down and it's getting worse week by week. It all started last year with significant drops in October followed by January 31th and March 29th of 2012. The site is being overtaken by larger brands that use cross-linking between their multilingual sites. One site dominates the sector with results #1 to #4 in many searches.

Drops:

2 word search: from steady #3 to #9-#10
1 word search: from page #1 to page #6 (dropping at a rate of 1-2 pages per week)

Here's what I've done so far:

Layout redesign for better usability
New CMS, 301 old urls to new ones
301 or noindex a lot of thin content pages
Removed some backlinks coming from my own sites
New high quality articles, 700 words each
Some new natural backlinks (getting more all the time)
Google Analytics
New faster server (but the CMS is still slow)
New meta description for the index page, meta title unchanged
Social media links
rss feed

The redesign didn't affect the rate at which the positions keep dropping. I haven't seen any positive movement in the last months.

I can no longer afford to buy new articles or web-apps to the site or do paid advertising online or offline

Should I continue link building (slow and time consuming)? Or forget about the site and move on with other projects / things in life hoping that some day it will recover... which is unlikely since the niche is dominated with big brands or 10 year old sites which aren't penalized for their hundreds of unnatural links.

I can give the url in a private message if you are interested in giving me a critical review.

this is the crazy thing with penguin and panda...google claims they want to give the small mom and pop site a chance to compete, but what they don't know is that the small mom and pop sites are the ones who do the most link building to compete with the big guys...

google is killing small business...google is not our friend...

Stupid question: What is WH? Are you referring to white hat? If so, that may be your problem. You can't use a white hat strategy to compete with sites employing black hat strategies (or sites that simply outrank you in pagerank). It's that simple. You'll never win.

PR5 is nice, but a bump up to PR6 would at least maintain your current keyword rankings, and prevent them from continuing to fall. A further bump to PR7 would make an enormous difference in your rankings (you'll not only get your rankings back, but you'll reach new high rankings for your keywords).

One legitimate pr9 link (with low outbound links - not some blog comment on a pr9 page with 500 other comments/links - I'm talking no more than about 25 outbound links on the page at the most) should do the job nicely. That should bump you to pr7 or possibly pr8 depending on the makeup of the rest of your backlink profile. Similarly, a pr8 link (or it might take two pr8 links) with low OBLs should bump you to pr6 or possibly pr7, again, depending on the strength of the rest of your backlinks.

Now, that'll require a monthly budget of $650-1250 or more. However, the beauty of it is that if you have multiple websites, you can link from your newly upgraded pr7-pr8 site to your other sites and pass the link juice on, giving them a huge bump in keyword rankings as well, so 1-2 high pr links can quickly and easily pay for themselves.

If your interested in trying this, PM me. I'm a link broker and have legitimate (none of the 301/redirect or other fake pr tricks) pr8 and pr9 links available. I'm testing a new marketing idea for my service, and based on this, depending on what niche your site is in, you may qualify for a 50% reduced monthly rate. Let me know as soon as possible, as these links are in high demand and go quickly at full price.