Invariably, my clients who sign off on their Wills and Powers of Attorney exhale a sigh of relief. I am not convinced that's necessarily because doing so guarantees them more monetary wealth. In fact, most of my time with clients is not spent talking about money at all but about what it represents.
See, the jury is still out on whether more wealth means more happiness (see http://www.forbes.com/sites/susanadams/2013/05/10/money-does-buy-happiness-says-new-study/). What has been settled for a long time, though, is that “self-efficacy” (Albert Bandura), the sense that what you do now impacts your future and the idea that you are capable of reaching your goals, is strongly tied to your sense of wellbeing. We also know from people like Mihaly Csikszentmihalyi that wealth beyond what is needed to meet your needs does not make a significant difference in your level of happiness, but a plunge in your net worth significantly decreases happiness. Another fact: giving to others can give you a happiness boost.
Taking the psychological forces into account, it totally makes sense to me why the act of seeking professional help to complete legal documents is not entirely a financially motivated exercise.