Given how little time and effort that takes, I don't see the issue. Who knows what screen readers, minor browsers and the like you might encounter?
I would say yes. That seems to be the Minimum Level of Quality (MLQ) that you should obtain for your MVP. If I recall, it's kinda easy and simple to do. So, why not.
I would test the website in various browsers on different platforms. Windows, Mac, Linux etc. As well as in various smart phones and tables. If it renders correctly and works then I don't see a reason to spend time validating to every w3c standard. There are even Google sites which don't validate entirely.