Why does "some people don't know how this works" make it less trivial?
Of course a salt. Not sure why that would make hash collisions easier to take advantage of though. Presumably you use a good hash function.
But there's no paranoia involved. It's cryptographically quite simple. All you need is a hash function.
Contrast with all of the governments and all of their security agents and such and nobody really trusts that it's secure.
It is if you use a commitment scheme. Such a thing allows you to commit to a value before revealing it. So you go in two steps -- everybody commits, then everybody reveals. Nobody can change their value after committing, so nobody can base their values on others' values.
I think you could perform the dice rolling experiment without any need for security against tampering. To generate a random number from 0 to N-1, have every interested party generate their own number (roll their own die), then everybody reveals their numbers together and the group adds them all up and takes the remainder after dividing by N.
With that procedure everybody should be convinced that the result is at least as random as their own number.
The point isn't to make it more random, the point is to make it more trustworthy. You can participate in the process and be confident that the result is random without having to put any trust in the other participants.