They're not really unknowns, though.
With every player you discover, you already know their current ability level. Those numbers do not change with scouting. All scouting does is reveal potential.
If an unscouted prospect says he has 65/65 power vs. lefties and righties, then he will definitely start with 65 power vs. lefties and righties. What you don't know is if the projected number is accurate. A true 65/65 might be a D potential. But if your scout finds he's actually 65/80, you could be looking at an A potential power hitter.
I don't know if this is common knowledge, but after I realized the current ratings are accurate and do not change with additional scouting, basically every player I draft now is already in the high 60s/low 70s overall. If you focus on scouting only guys who start off with usable skills and ignore players who will inevitably be drafted with an overall in the 50s, you can typically fill your whole draft with guys who will be MLB-ready in a year or two and have solid potential.
My last draft had like five guys with at least 72 overall and at least 77 potential. Several who will be cheap bench options. A couple who will be quality everyday players soon.