Getting ready to have my first draft. When I show the top 500 prospects, after about 350 prospects the projections are all "?". Seems like after about the 75th ranked prospect, most of the players don't have ML quality ratings. So my question is, are some of the "?" players potentially very good? If so, then is it worth ranking some of them in the 200s or even 100s on the off chance of drafting them? does that make sense?

Potentially, yes.   Worth ranking, no.   Someone else sees their ratings so, if they're worth having, you're not getting him in the 4th round.

As a general rule, only rank the players you expect to be BL players.   Maybe they're fringe D-catchers but they're worth ranking.   Ranking a pitcher with 28 control and 43/38 splits is just a waste of time.   If you see 75 potential BL players, that's a lot.  I'm usually somewhere between 40-60.

Ok...good feedback...yes, I only truly ranked the top 50 and then moved some guys between 50-100 around