Welcome to Gaia! ::

We're weeping at the fact that the Digimon World DS series has yet to have wi-fi battling, but as to your theory...

I'd say it's a possibility. However, I wouldn't so much see it as "growing up = getting stronger". But more like, "I've done this before, I know how to do it." Kinda like driving. You don't become more experienced at driving because you're getting older, you get better at driving because you drive.

So I'd say use of the crests in relation to the relationship of Digimon and Human becomes stronger over use. Such as the battle against the Dark Masters. At first, when WarGreymon and MetalGarurumon took their stand against Piedmon that they royally got their a**'s kicked by an evil clown. But later on, as they more constantly warp digivolved to Mega that they steadily became used to their powers and subsequently vanquished the Dark Masters one by one.

Especially that of Puppetmon. Matt was certainly in his loner rebel mode going against the grain of the Tai and the grain. But still, in a very anti-climactic way, MetalGarurumon disposed of Puppetmon very simply.

So I'd say the Digimon growth in terms of the powers channeled through the digivice and crests has more to do with constant use and experience in the use coupled with the relationship between Human and Digimon, as opposed to the mental state of the Human himself.