Hi,
I've used both over the duration of 1.5 years (iPad) first, and have had both available since the iPad mini came out. I hardly ever use the iPad anymore.. The mobility (weight and size) makes it so much more handy. I have to say though, that if you read a lot in long stretches of time the mini's lack of a retina display will annoy your eyes - its simply not anywhere near as crisp as the retina. When/IF the iPad mini 2 will have the retina - that would be awesome!!
As for your specific question about charts and manuals. iPad mini does the job just as well as the larger iPad - but its so much handier to carry around. So for the "work" bit - I don't doubt.
Anyways for a bit of manual look up/study, a bit of news paper and magazine reading the mini has made my iPad redundant.
I have to remark that some magazines like Flight lack the application option of letting you enlarge the fonts - which kindda makes it painful on the mini - wheres newspapers like FT and magazines like The Economist will let you enlarge the fonts - which really makes no need for the larger screen that the iPad has.
Good luck.