What exactly do you feel like you are missing out on by not using facebook? And whether a linkedin account is beneficial is dependent on what kind of work you do.
I meet a lot of people who in theory are 'one friend removed' from my social / professional circle. (Based on shared university, job, or hobby).
The ultimate goal here is to meet people who can help my business, either by funding it, working at it, or hiring it.
Maybe the trick here would be to profile these people like you would when doing demographics to know who your customer is and then then you will know exactly who you are looking for and where they are without having to waste time on social media.
I'm with you so far, but wondering if these channels can be cheaper / more effective ways to access that audience. In part because it's a platform people are looking at, and in part because these platforms leverage existing 'once-removed' circles of trust.