Your site load times - seem good from a UX perspective, so not sure if just a page speed tool is gonna do much for you on the SEO front.
Also just adding social, does not mean it will work 
Overall (without really looking into your site at great detail) I would say the "fundamentals" are correct - Just as you said, focus on generating more high quality content relevant to your niche (not necessarily just about grinders)
I think this is one of those tough social niches, as generating buzz about grinders might take some real thought! (lol what the heck is a grinder!) But definitly think you would be in the realm for some whitepapers and technical documents that could get some good pickup in your industry if well written, engaging and informational.
Your name is earthsaver, Is your equipment green? That could be a roundabout route you could take - instead of just trying to talk about Grinders themselves as products.
From a purely SEO perspective - your best friend and associate is research!
http://www.seomoz.org/beginners-guide-to-seo
PS. Not really a SEO killer - but alot of your scripts and CSS are inpage - this could be why Brent suggested page speed - as having this code adds load time, and it makes it sometimes more difficult on G-bot - but I would not loose to much sleep over it if this is something that cannot be easily fixed at this point (but could become an issue at times of heavier traffic loads)
One thing from a marketing perspective- the Message on the Homepage is not clear, what a grinder is and what it is used for - but I would assume this may be because if you are looking for a used grinder, LOL you probably know what it is!
sorry