Can you rank well by depending only upon on-page optimization for a non-competitive term? In most cases, the answer is yes. You don't have to go on a massive backlink hunting spree for a term like yellow cheeta eyeglasses. Ok, you think, so what? Only the competitive terms matter, right? Wrong! Ranking well for non-competitive terms can bring in traffic, while you work on gaining backlinks for your competitive terms.
Putting this into perspective, what if you were a seller of eggs? Would you throw away all eggs that were not Grade AA quality? No, you would grade the eggs as A or B quality, and sell those eggs at a reduced price. Think of your keyword terms as either AA (competitive) or A/B (less competitive). Utilize simple on-page optimization for the A or B quality terms while you spend more time ranking well for AA quality terms.
Put up ten or twenty well-optimized pages focusing on non-competitive, but related keyword phrases. Those pages can be bringing in visitors, while you are spending time acquiring backlinks for your competitive phrases.