The way I see it, the quality of an investment depends on its expected value: chances of success X magnitude of success. No traction (yet) doesn't necessarily mean that chances of success are low.

For example (not to self-promote, but my situation is a applicable), my website solves a real problem. Student reviews of colleges ask questions that are too broad. Applicants want more information. I ask more specific questions that provide more information, and thus solve the problem. I've shown that I could get reviews because I paid for them for 3 pilot schools. However, I need a seed round to pay for reviews at the other 297 schools. I don't have traction yet, because I need reviews first. But people say I need traction in order to get the reviews, which is a big problem.

See https://www.dropbox.com/s/8cuu8ztl4srfgb6/Questions%20Comparison%20pdf.pdf to see the questions that I ask compared to the ones my competitors ask.