SER is an excellent tool for building PageRank and authority, but it's only part of the equation. Here is my analysis:
1. You must build Trust. Google's algorithm is putting more and more emphasis on Trust to combat automated link building. Automated link building doesn't help with trust. I love Majestic's Trust Flow metric. Even though this is a contrived metric by Majestic, it is believed that Google also uses a version of trust flow. Trust starts with Google designating highly trusted seed domains that will never have Spam. irs.gov, harvard.edu, nasa.gov, etc. Trust is passed from these sites via outbound links. Sites that have links from trusted seed domains can also pass trust, but less of it, just like PageRank. For trust, the next best thing to a .edu or .gov link is a link from a site that has a link from a .gov or .edu. Every site in the chain from the trusted site (ex: Trusted Site=>Tier 1 Site=>Tier 2 Site=>Tier 3 Site) can pass trust, but far less as you move away from the trusted seed domain. Google found that the further removed a website is from a trusted site, the spammier it gets. Solution: buy links, or hand build them, but always focus on Majestic's Trust Flow Metric. If your site is CF: 30 TF: 3, you need to get some powerful links.
2. You must build relevance. Google's algorithm is also putting more weight on the relevance of links. If your site is all about Widgets, it would be really, really helpful to buy or hand build links from sites that are authorities on Widgets. Once again, use Majestic's "Topics" metrics for finding potential sites for buying links or building by hand.
3. You are getting out-spammed. If you aren't using a verified list building service like (shameless plug) www.serlists.com
and a decent server, you are losing the battle, because you can bet that your competition is using them.
4. No social signals. You also need to mix in Facebook Likes, Pinterest Pins, Google+, etc. Plenty of services on other forums.