If you have ever played on an EA (not OSI) shard, you'll notice that there are (last I counted) 32 inhabited towns. Then there are maybe 3 or 4 un-inhabited (un-guarded) towns...
How many of those towns actually have playes in them at any given time?...
Maybe 5.
5 or 6 out of 32 towns actually have any players in them at any given time.
Why? Because even with the 10,000+ players online at any given time, they usually don't stay in town very often, and when they are in town, they like to be in the same town as most of the other players... So what you end up with is 2 or 3 heavilly populated towns, 2 or 3 sparsely populated towns (where anti-social players like me go) and a whole heckuva lot of empty ghost towns.
And that's with over 10,000 online players at any given time.
Your shard probably, at it's peek, might have 100.
Think about that a while.
Originally when OSI still existed and ran the shards, they only had one world and 14 towns, and only 8 that a newbie could get to. On top of all that, they had fewer shards back then, so there was usually a minimum of 30,000+ players online at any given time. What did that mean? PEOPLE ACTUALLY SAW OTHER PEOPLE!!! OMG! CAN YOU EMAGINE THAT?! ... heh... Yeah.
I remember every street of every town had 4 or 5 people on it. It was absolutely wonderfull because it made the towns actually feel like TOWNS and not just ghost towns. Now your lucky to see 4 or 5 people at the banks....
It sure was nice when a town felt like a town even without all the NPCs...
And you want to just amplify that effect emensely!!!!
Do as Ryandor said, if you must have multiple worlds, split the main map up into a bunch of tiny worlds (very possible). You don't need to go and make it even bigger and more sparsely populated than it already is, especailly for a player-ran shard.