Twinks making economy great for other twinks? I'm just gonna be a realist here and say that will literally NEVER happen.
Every twink hub in existence will always have inflated prices, because it's simple economical behavior. Even IF twinks actually came together and made easily affordable market prices, some non-twink AH flippers will eventually just catch on and jack up the prices anyways.
It's a nice utopic dream, but that's all it'll ever be, because there will always be people who are looking to get ahead, and that's just not in economic terms, that's literally human behavior on anything. Factor in the anonymity the game and the internet gives you as well and you'll see that it's simply not possible.
This is why the ideal server is mixed so that you have fair prices.
You have people who don't give a shit or are down-right un-knowledgeable about twinks and post items for a steal, then you have the middle ground and then you have a select few that actually plays on the niche twink market.
The benefit to a twink hub will never be the economy or item availability. Those would be the exact drawbacks to a twink hub.
The benefit will be guilds, community, peers. If you want good economy, the best is to find servers that have a very diversified and active AH. To my experience, high pop, non-twink hub, RP servers fit that criteria perfectly. People constantly sell EVERYTHING for transmog and whatnot and usually at an absolute steal if they don't factor in the twink or rarity aspect.