Here are my two cents:
1) Make donation weapons tradeable. This increases a demand in the market, as not every player is able to donate, but every player is able to acquire these extremely powerful weapons. Most players, wanting to keep up in PvP, will purchase these items from donators. There may only be a few donators pumping these items and awakes into the market, but they will be spending hundreds of dollars to further themselves in-game.
2) Add powerful cash shop items. The Scroll of Unbinding (which is already present in eFlyFF) is a great tool for players who want to sell their soul-linked items. Also, the Font Editor (another cool item in eFlyFF) gives players the ability to change the color of their shouts, which is invaluable when marketing. A bright blue shout among light red shouts really stands out. Again, in eFlyFF, there is an item that spawns monsters like Red Meteonyker and Clockworks (only available in one of the Alchemy events). I'm sure that the devs could crank out items like this that spawns rare bosses like the Basilisk of the Great Maw, and put these items in the cash shop. In addition, if the server diversifies to have unique items and scrolls that no other server has thought of rolling out, then more players will be attracted here, bringing in more possible revenue.
3) More events. In my time on Fly for Smurf, I've only ever seen an event happen once. In comparison to some other servers, which have a few invasions a day, this server seems very dull. Events that spawn rare, high-in-demand monsters like the Basilisk of the Great Maw would bolster the population to be more active, and lowers the prices of alarmingly expensive items, which scare away new players very quickly. The server should, of course, do other events, like Hide and Seek, bringing a GM a certain number of items, Simon Says, and the like.
4) Custom mobs. I'm not saying to completely redesign new mobs, but instead to take some old ones and tweak their levels a bit. For instance, the Desert Spirit of the Sage is level 146, which makes leveling past that level very hard. Increasing the levels of monsters in the Bahara Desert, or in Traseia, would make leveling past 145 easier. Most people who siege or PvP are level 150, so this
5) Fixing lag. In Flarine, the lag is so bad (for me) that, even on the lowest settings, it takes around five seconds for the server to register that I have bought, sold, or moved an item. By lowering, or even removing the spawns of mobs that no one visits, such as places on Flaris (everything from Mushpangs to Feferns), Saint Morning (just tweaking the spawns a little), and Darkon 2 and 3 (with Darkon 2, mainly just the stuff past Clocks, and basically getting rid of most stuff in Darkon 3), the server can become a little more lag-free, as it will not have to make calculations for them anymore. Practically no one battles those mobs. This will help to make the starting town less intimidating to newcomers (possible donators), and, by having less lag, gives them the impression that the server is of extremely high quality.
And that's it, for now. If anyone has any reasons why these suggestions wouldn't work, feel free to post. Honestly, this is my favorite server for a while, which is really saying something, and I would love to see it succeed.