> I'm wondering if, rather than transform yourself into a 
  > magical-unicorn designer/hacker - it might be better to 
  > get solid at development, solid at design, but aim to 
  > only get good enough that you can manage people who are 
  > better at you in those areas?

Depends on your definition of "better". The market clearly treats the three skills (dev, design, management) as separate things, so really you don't even need to be "solid" in more than one if you define "better" as "above average salary". If you define "better" as "can move the project forward without finding another person to help", then becoming a "superhero" is what you should do.

Note that "we're still figuring out what this product is" stage startups really hope to find these "superhero" types, as they can litterally breathe life into a product by themselves. Larger companies can't depend on hiring people with all skill sets, as they're too rare.