I'm not sure the big bang is always testable. The question I'd ask myself is, "How satisfied are we with the velocity of our business, given my goals?" The goals here are important. One person's goals might be around lifestyle, low-effort income, etc. Another person's goals might be around big $ liquidity or getting enough traction/growth to attract angel funding.

If growth/success is not measuring up to one's goals, you have two choices. You can A/B test your way up or you can do something dramatic (hire a salesguy, pivot your product or positioning, etc). I think a lot of startups with big dreams and crappy growth dive in with A/B tests when they should be figuring out how to change how people talk/think about their product(s).

You're right about being expensive. The scarcest fuel for most teams is optimism and confidence. One or two failed pivots can be devastating.