The problem you'll find (I've found) in this case is that management in many of these "startups" expect a certain kind of ... ahem... motivational/authoritarian structure ... that lacks effectiveness or sense with someone who has paid off their mortgage and is mainly there in order to ship things and enjoy crafting software.

Put it another way, there are people in every company whose reasons being there can conflict with the motivations of an engineer with the priorities you describe. Often those people end up being your manager.