Believe it or not, the suggestions you asked for have been in the game for
years. They just might not be how you expected.

For example, let's say a newbie is out killing newbie monsters. Most times,
the "boxes" they drop will be pouches -- no lock, no trap, and probably
carrying little more than mowgles. This is the "don't lock my pennies up"
analogy you mentioned. But, once in a blue moon he might find a "turbo box"
for him, a locked wooden box with better coins (silver, gold, etc). For a
newbie, this is a nice drop. Unfortunately, a newbie's str, weapons, and
skills/spells are rarely suitable to opening locked boxes on the first try.
It'll probably take him a few tries, and if the box happens to be trapped, he
stands a half-decent chance of geting damaged or killed. But, for the random
cash potential, for the newbie the risk is about right.

Switch to a highbie. Highbies kill bigger monsters, which usually don't drop
pouches but locked boxes. However, locked wooden boxes should pose little to
no problem to a highbie, armed with a better strength, lava blasts, or the
like. They will probably rip the box open in one or two tries, and even if the
box was trapped, it doesn't have a very good chance to go off. Should the
highbie get a "box" from a larger monster, however, it will most likely be a
metal safe or chest. These tend to be very hard for even a high-level player
to open on the first try. The same overall result happens: the cash (and other
stuff?) inside is better, but better guarded, and the opener stands a higher
risk of damage or death.

Most everything else you asked for has been in the box code for years.
Frequency of traps, as well as the damage of the traps, does indeed go up
based on the "box level". That does not mean every wooden box has a poison
needle and every adamantium safe explodes -- there is a spread of randomness
there. But boxes have been the great risk/reward gamble ever since they were
put in before I started playing. Treat with caution.

Shinarae "wanted: box opener" Lluminus

P.S. I heard there are ways of opening boxes that have a greatly reduced risk
of death. Every party of 5 or more people should have one.