The random loot is a great idea and wish more games would implement this. The game does have "certain events" with designated items so everyone will surely find something for each class guaranteed.
However, I would also suggest designating certain chest or boss loot to be tied to the percentage for that particular skill tree. For example if you are all caster than you should have 80% chance of getting something that is "ideal" for caster and 20% other.
If you are half melee and half ranger than 40%/40%/20% respectively.
As far as locked chest is concern, I don't think it is a waste to put 5 points into it. I have found some pretty good stuff in them in comparison to some other games like Dragon Age, in which lock chest mostly have useless or obsolete items.
