And if you ever get so big that people start writing bespoke software to break your CAPTCHA, then investing some more engineering effort into it will quite likely not be a problem.
Of course reCAPTCHA is also still vulnerable to the use of a mechanical turk so even giving away your users' data won't save you.
I've come across a CAPTCHA on a website I was scraping that was absolutely terrible. It was 10 multiple image choice answer, with a question to click the image that had "X". Their implementation didn't even have a nonce, so I would just attempt every single answer and get past it.
Of course reCAPTCHA is also still vulnerable to the use of a mechanical turk so even giving away your users' data won't save you.