It may sound a bit boring (sorry), but I want to introduce the concept of "calculated risk". On an aggregated level I personally don't do extremely risky things in domaining, and have no desire to do so.
Many domainers will never sell all of their domain names. The entire portfolio must offer possibilities to realize a healthy mix of small, medium, and large sales, over different periods. The calculated risk consists of making good estimates for your domains in each category and their probability of return. The total annual renewal costs are an "acceptable risk", even if you have to wait one or two decades before a domain gets sold for the amount you're mentioning in the original question.