Agreed. The Vaults are not really an Easter Egg, nor will the fact that I cannot enter the vaults make me want to play it more and more. I think most players will try what they can, become frustrated, and either not bother entering the vaults when aiming for 100% kills, or look through the wiki and forums if they want the badges/loot. There are other places where the player has to think and prepare largely ahead of time (Full win, DS, master traits), but none that I know of require so many items, so much luck, and so much risk. In the even that you actually make it into the center, you'll have an awfully fun time telling the denizens that they must leave... in bodybags. The risk/luck/preparation involved in entering the center vault does not outweigh the reward, IMO (few items, rarely exotic or unique in center).
So, we could make it easier to enter the center (walk through lava or something), or make the Vaults more rewarding, more worth the 5 PDs likely needed, and akin to the name; "Vaults" make it sound like awesome treasures. Guaranteed Unique maybe?