You are not expendable. Sure, you might be clumsy, weak and not particularly bright, but you still decided to venture into this tower to help others.
That alone makes you worth saving.
You will not fail, Yulia. I will not allow it.
Still no Alide? That is quite dissapointing.
Naturally you should take the key.
As for the armor, given the floor's motive of greed it certainly seems a bad idea to take it, but let's look at your situation
-the monster of the floor is defeated
-you have already disabled the trap in the wire room
I imagine this armor would work in tandem with these two hazards and slow you down/injure you as you are lugging it back to Dahlia, since both are gone the situation changes considerably.
As such I vote for taking the armor with you. Provided you are even strong enough for it.If not you can settle for the helm alone, Bring it back to Dahlia and see what you can get for it.
since the last map wasn't very accurate here is a new one