So about the mystery boxes, I feel like the things you can get from
the mystery boxes should be a bit more valuable, because I have to
rumble my pokemon for 12 hours to get the boxes and the keys and I
got 8 berrys that I have never heard of, unless I am mistaken of
what I got from that mystery box and that berry can only be found
through mystery boxes.I feel like the mystery boxes should always
contain something that is at least worth 2000 pokedollar so at
least it is worth it to go through all that trouble.
Mystery boxes not only have berries and non-value items but also
they have rare legendary summons in them.
These legendary maps' price is 15 times the price of the mystery
pair. And of course, getting them is also very hard (you need
luck).
And also, as your rumble level will increase, you will start
getting more and more items.
The luck of getting these items in mystery items cannot be changed.
The items which are valueless have no price and items which are of
high demand (like summons and maps), cost high price. Every item's
price depends on the demand. Even a berry when on high demand can
become very expensive. Random items are placed in Mystery boxes and
also, mystery boxes don't know what's rare or which are of demand.
:)