Yes, one does need in-bound links to to improve SE ranking.
At least in the case of Google, every site that links to you is counted as a vote. Links that are on-topic, and from related sites are more valuable that those created using linkfarms.
One way links help you expland the connectivity of your sites' own little graph beyond the nodes participating in a reciprocal lin exchange. Therefore, on-topic one-way links are considered very precious!
Selectively establishing on-topic links to your site, and including quality outbout links from your sites to other related sites are important to overall SE ranking.
I do not think link-farms do much good over the long run. YMMV!