I've never coached in the amateur game, nor have I been part of that environment. But from watching from the side, talking to players - 20% high school/summer leagues, 80% college age, the number's game as you call it is kind of haphazard at best.
I say this from a game plan perspective, and so-so from a scouting perspective.
From a game plan perspective, there's not much one can do to plan and then depend on that plan enough to make things worthwhile from the get go. Level of play from one club to the next has such dynamic swings to it, the have-n-have-nots, pre-select teams even before the season begins and so forth. Now I'm sure there are exceptions and you'll probably get a good response here in that direction. But, from where I sat, it's rare to find a well planned number's game for putting a team together, reaching into the future about another team for competing against and the like.
As far as scouting is concerned, I go with personal observations, recommendations, and who the player competes against. That last one - who he competes against I would take with a grain of salt, if you will. Also, from a scouting perspective, the numbers that I get and those that others arrive at, are usually like night and day from those numbers arrived at by the amateur experience.
However, consistent performance of a winning club and even a player or two that shine regardless of the others around him are worth noting. In fact, a glance at the sport's page in your local paper - following a team or two, can be beneficial. Reputations of a man as a slugger, a winning pitcher and so forth I guess can be of help. But again, one must take into account who that individual or individuals played against to arrive at said reputation and so forth.
I'm sure others have a answer that'll be more definitive for you than mine. Good question.