Before arsenal stations came around, you had to plan wisely. You couldn't just take the equipment that worked best for each level, because you didn't have that many slots. If you had construct in D25, and beasts in D26, you had to either take weapons that could hurt both, or a weapon for each. With stations, you can take elemental weapons one level, and then switch to pierce one depth down. If you didn't have the ability to chose any weapon you have in every level, it would increase the strength of normal weapons. I think it would contribute to the difficulty and the planing part of the game to make the chance of seeing an arsenal station random for most levels. An example table for chances could be:
100% chance in starting boss levels, terminals, and subtowns, regardless of tier.
95% chance in stratum 1
90% chance in stratum 2.
75% chance in stratum 3.
50% chance in stratum 4.
20% chance in stratum 5.
10% (5?) chance in stratum 6.
Maybe sometimes the station could be busted, or maybe it wouldn't even be around.
EDIT: some of you seem to wanna flame. Of course, these values I gave do not have to be followed exactly and could be something like this:
100% chance in starting boss levels, terminals, and subtowns, regardless of tier.
100% chance in stratum 1
95% chance in stratum 2.
80% chance in stratum 3.
65% chance in stratum 4.
50% chance in stratus 5 and 6.
Also, the only reason why the chance gets lower and lower is because it is supposed to get HARDER as you go deeper. Sure, you won't need it as much the higher you go, but you don't need to revive yourself as much the higher you go too, right? Why, it is only 2 energy to revive in T1, and 10 in T3, and you need to revive more often in T3 then you would have to in T1. The only reason that it is like this is to make it harder: you can't die as much, or you will quickly run out of energy.
I remember those days. Times were good. I like this idea, whether it be out of nostalgia or out of want for more challenge.
When I think about it objectively though, here's what I'm seeing. On one hand, players would be encouraged to play more strategically, which is probably good for the community. On the other, players might end up limiting their arsenals to weapons/armor that cover all bases, which results in less profit for OOO.
Just my thoughts.