With the new tt cap, more and more people will want to train in vd2/vd3 for tactics since they can't stay in vd1 anymore and cyc/fatal/succubus are bad for classes such as wizards (and priests that chose to blast). If you plan on staying in vd2/vd3 for a long time, then you're going to need pots but you also will need argos tooth, mana metals, sand of start, klattu, or gazers. That takes up a lot of room in your bag which would be used for pots if you were leveling in say VD1. Also repotting is expensive since you need to pay the floor entrance fee again (for vd3 at least). Make VD items stackable so that VD2/VD3 is a more viable leveling area.
That or remove the "per room" free (such as pay 1 argos tooth every time you enter a room of vd2) but keep the fee to enter the floor. That would make wizard tactic less screwed compared to other classes at higher levels. (especially since wizard's mana doesn't regen as fast as cp does).