Do you think it's a bad idea to have a high-level conversation between the company and the prospective employee before assigning a take-home test?

That depends on the attitude you go into the conversation with and whether your take-home test can be automatically scored well enough for a coarse filter to reject the people who obviously cannot do it. It also depends on how many applicants you have. Spending half an hour per candidate gets onerous when you have hundreds, so cutting to the chase in a semi-automated way may be a better means of whittling the pile down than having a recruiter, founder, or hiring manager filter it based on conscious or unconscious biases.

I was highlighting that line because I think it indicates a subtle bias towards people based on background and assumes people are not making reasoned decisions about what they are applying to. I understand that there are tons of unqualified resume blasters out there, but I figure nearly all of them will either ignore the take-home or submit such schlock that it will be easy to automatically reject them.