There are only about 4 quests in Mycopolis, which isn't nearly enough to leave the area ready and supplied to survive the dangerous underdark.
Furthermore, it isn't even a Nature-Hub, given there is no quick way to reach it beyond a 10 minute boatride. I would suggest either more quests, or that the gear you can get in Mycopolis to help you survive is more reliably given. It gets old farming Shore Jellies quite fast. It isn't designed to be a nature PC hang out for the very reason it is very easy to leave, but a pain to return to (no one wants to spend 10 minutes on a boat every time they want to hang out in this cool area).
It's not supposed to be any sort of hub though either, bear in mind. The npc's do not want you to linger there. They want you gone as soon as you are able to be gone and will help you get on your feet so that they can safely give you the boot. The place is already packed and overcrowded and not meant to be a hang out spot. Having a little variation in the items provided from the shore jelly grind would be a good thing though, but if someone really wants to benefit they'll still have to leave the safety of the nest prior to level 6 and explore the wilds of the underdark.
Precisely, so here's the situation really- add a few more delivery quests that can act as a underdark tutorial, introduce them to elements in the wilds that might not be all that obvious otherwise- introduce them more to Myconid ways of life, and so on.
Just a few thoughts on the matter.
Mushroom safety cloak