I agree with Thoraion, That dementlieu should not be the high level zone but rather it should be either a medium level area or better yet, outside of levels. I prefer it being outside of levels. The type of rp in dementlieu can be for any level, not just high levels, sure there are the gangs at night but the main rp of the port a low level could achieve just as much as a high level could achieve. But at the same time a high level can do it too. There shouldn't be a level requirement in Dementlieu for the rp, as the horror there is physiological.
Dementlieu should be a place where levels don't matter, save for skill checks IMO. You likely will not be fighting any sort of monster in the port as the horrors there are all human, all to human for it is the evils that men do. However, the biggest issues with the Port IMO are as followed. Also about levels, if it is to be a high level area, why is there a little low level area there where you can fight dire rats?
First it takes a while to get there, since it does take a while to get there, that does distract people from going there. My suggestion having a portal in the OOC area to Dementlieu with a sign in big bold letters saying NOT RECOMMENDED FOR BEGINNERS, or something like that.
The second issue, is that it is hard to get money there. Plenty of ways to spend money there, but not enough to get money there. My suggestion is to have some minor delivery quests, ie, bringing holy water to the church of ezra, ink to the printing press, similar things. You wouldn't get a lot of money but you should be able to support yourself in the port.
the third issue is lack of people and DMs. yes, this is an issue IMO, but this is harder to solve then the other two issues. My suggestions are simple, one more people should try to apply for the DM team as they do seem to be interested in people becoming DMs who are willing. Also The dms should try doing some shout outs for the place, like heretic's awesome shout outs for barovia. PCs should not be afraid of doing some events them. Just attempt to do something to create something and likely more people will come there, but no one will go there if people don't try stuff.