I used to play gRO quite often, and I still hop back from time-to-time... but it saddens me how gRO seems to be slowly losing its shine.
In any case, I'd like to add in some pointers as well. Especially on how the in-game economy works.
As Everade said, a new coin-exchanger sounds great. I suggest that coins may be possible to be farmed fairly easily, but still challenging and fun, (i.e. from monsters, or regular ingame-scripted events), and that they can be exchanged for some spiffy end-game items. It is key that they are not just for good-looking equips or figures, but extend to maybe cards and God-item ingredients as well. Things that new players would want to have to join in the action.
It'll be nice to have new currency coins to exchange for a useful card. Much like the Kafra-shop for example. It's silly that players would have to grind for weeks just to get enough zeny for a good PvP-worthy card like Deviling or Turtle General.
Newbie-packs rental items would be a great idea as well. Say, i.e. a weapon which works like Ice Picks, but with a 30% dmg reduction, character-bound, expires in 5 days, armor which gives you +50% HP, -50 DEF (e.g. like Tao, but significantly weaker). Not exactly these items, but the idea is there to reduce how handicapped new players would feel in comparison to the new players, and to let them have a taste of the action.
As for the economy, I think it is solely irresponsible to blame it on the players. The admins are the ones who made mithrils highly useful - since they are sought after for END-GAME items. The use of mithrils was dictated by the admins, so it is natural that players would crave end-game equips. I suggest that the new currency will allow one to exchange for mithrils too, maybe an hour of hunting new coins can net you around 2 miths?
The server provides the necessary structure for an the economy to flourish (or in this case, denigrates). If you decide to make mithrils highly useful, and zeny to be pretty -meh-, you'd expect miths to net very high margins. This sorely needs a change... albeit not a change in players' attitudes, because you can't change collective behaviour of player, that just doesn't work. But you CAN change the system, and in this case the players' behaviour have to change accordingly.
New methods need to be developed for players to attain good PvP-worthy equips. One of the ways will be to peg these PvP-worthy equips to a new currency which can be obtained via farming.
Let's call these coins Gatherings. Gatherings may drop from different monsters in the game, i.e. Poring (0.10% droprate), Goldrings (1.50% droprate), Abyss Lake monsters (1.50% droprate), MvPs (100% chance of 10 Gatherings). During seasonal events, say Christmas, Lutie field monsters may begin to drop them as well, and Mi Gaos on Chinese New Year etc.
Gatherings should be able to work like Kafra Points (I know people won't like this, but since end-game equips are available from Kafra Shop, this is necessary not to alienate new players. As the server population grows, naturally you'd have people who will still donate). Maybe 1 hour of hunting nets you 90 Gatherings, and if 1 Gathering = 1 KP, and you'd need 900 Gatherings to get a card like Deviling - 10 hours for a good card, spread over 5 days, sounds good to me.
Zeny sink. Too much zeny in the game leading to hyperinflation... maybe it is possible to introduce more quests to drain out zeny from the system. One way you can do this is, is to charge a fee for using the coin-exchanger, i.e. every conversion of 1 Gathering costs you 100,000Z. For every Deviling Card (900 Gatherings), 90m is drained from the economy. Main point is to drain zeny from the remaining players who have HUGE reserves (in the billlllions).
just my 2 cents. will love to see the server up spiffy and popular again.
edited for some grammatical errors