From what I've read about coffee grounds is that they are low in nutrients (almost everything nutrient wise) but are like using bark in a soil mix.
As they break down they lock up nitrogen from the soil they are in.
Once they reach a certain point they start releasing it back into the soil like bark does.
Natural time release ferts...

They also hold a lot of water which can be good...

By themselves,straight from Starbucks they are pretty nutrient deficient in general and depending on how much water was run through them to make coffee they really differ from each other , from source to source(resturaunt or coffee house) because different coffee brewers work differently-different temps and amounts of water were run through them etc..
All coffee grounds are not the same.
Even the coarseness of the grind makes a differeance.
Ask a coffee addict/connoisseur...
Worms eating them only makes whatever nutrients that are left in them more accessable to the plants.
So depending on how much nitrogen the coffee grounds obsorbed while breaking down is what becomes more easily available to the plants as worm casings along with whatever else the worm eats at the same time.
Bannana Peals are supposed to be high in Phosphorous and or Potasium.
Blossom drop isn't usually caused by too much nitrogen.
Nitrogen can prevent Blossoms from forming to a certain extent but doesn't cause drop.
Ferts high in Potasium and Phosphorous are better for blossom set and forming also root health.
A lack of Calcium causes blossom drop most of the time.
A lack of calcium can be caused by PH or just a lack of calcium in the soil.
Calcium insuficiantcey can also be tied to an overabundance of magnesium also.
Both need a slightly acid soil to be available to plants(same with iron).
There is more to nutrients etc. from organic additives in soil and compost but above is a generalisation about coffe grounds as far as I was able to find from gov. and college ag. site studies.