Sad Truth
I think the server population is decreasing because either people are finally moving on from EQ, or a lot of the reasons SoD emulated the 'EQ Feel' are gone. We all knew this was going to happen one day - we are complaining about issues more recent mmos have taken note of and 'fixed' - the result is everyone being uber instead. For the time being, I personally don't think there is a black and white fix for this issue. More content is the most obvious, or simply more quest options, but bare in mind this is for a server with a peak of like 300 (half of em boxes so like 150 lol) and limited staffing... so tbh, it's kind of a pipe dream.
For new players also, ive personally tried to get new people to play with me, but its extremely frustrating for noobs to try to get the hang of the game without being heavily scrutinized by people who invest 8+ hours a day into this game for being 'bad'. Instead of helpful suggestions, the common process is if someone doesn't know a specific tactic, mob strat or ability they're automatically criticized instead of any effort being given to help them learn otherwise. This discourages learning process and frustrates new people. The server reeks of this elitist attitude, and most new people now quit before they get their 1st aa because they're not neurotically fixated on SoD to the point of it consuming their entire lives...YET.
It also doesn't help that the game is 100% free... which always attracts a certain number of 'colorful' characters.
Also...as others have pointed out, some of the quests and tasks are just too much of a timesink. Yes you can always NOT do these, but lets be honest - thats the point of eq - get phats.
Many of the hardcore players will burn out from this timesink and quit or 'break' for awhile - and for new players, SoD is a hard sell as it is - more time required for less rewards, and far less to do than other online games. The charm was the more mature playerbase and the fun you had with those people - and the community for lack of a better word has become pretty douchy in the last little while.
Something for 'fun' sake I think would be neat is some form of PVP - not 100% serious, maybe just -some- incentive to bring some excitement in. I know classes are not 'balanced' in eq for this but it may give players something to do with their phats - perhaps make rewards illusion clickies or fun items - just throwin it out there.
All in all though, Everquest, be it Live or Shards or EQEmu, whatever form it is - it's a dinosaur. And we all play it because for a lot of us EQ was our first mmo experience, and we chase that feeling of progression, or we find another MMO hasn't given whatever 'feel' EQ has (Every week in ooc is a 'remember when' moment from Live, FFS!)
However, I think everything has its time in the sun, and maybe we should consider the fact that the sun has set on this dinosaur.