Instead of salivating over size, scouts should be focusing on a player's actual strength. And when I say strength I don't mean just upper body and arms, but also legs and cardio-vascular. This is a very important element when scouting smaller players. I have just talked about the importance of strength above. Michael Peca is a feared body-checker despite his small frame precisely because of his great timing and control.
Proportion can also be very important.
Finally, judging someone as young as 15 or 16 based upon their size can be dangerous. Such players are often your classic late-bloomers. Noting the physiques of parents and older siblings can often help in projecting full sizes. Conversely, some players who are considered big at 15 have often reached full growth. It can take a long time to take the blinders off of scouts and coaches when it comes to perceptions about players.