There are two things I do with some altered states on my game. First, is base stat changes. Even if it is a debuff, some of them actually raise one or even two statistics (if you want to poison your character to raise his strength by a 10% while costing you 10%HP per turn, you're welcome to do so!). Of course, real buffing states cause major increases, but there is it, if you want to take the risk, since you can stack even three poisons and three ATK buffs, making your ATK stat raise to something close to 220% (well, those 20% from poison don't seem to pay off!). It also lowers defense a little.
The idea behind poison raising attack is because some poisons can affect the mind state. So, on this case, it causes a lesser berserkr state, in addition to the steady body degeneration.
The other thing I do with altered states, is element weaknesses. First I gave each element one state. Poison for example is the earth elemental state (some poisons are just certain kinds of earth). Burn is for fire (which causes smaller damage over time but heavily cripples defenses). And so on. So each of these states raise damage from that element.
I also made a heavy magic booster which lowers 5%HP per turn, but makes you weak to Light. I've listed it between the pregressive damage states because it will be used by monsters. In my game, if any battler has 0MP, they die (Dry status).
I also have a frozen status. It works pretty much like Stone from Final Fantasy, it's treated like death, without lowering your HP to zero, and raises your defenses to 200%, but your character can't act. Difference is that you can cure it by using fire attacks on your character (or if your opponent randomly chooses to do so, nice!).
My hypothesis behind all of this is that, there is no completely black or completely white status. Beneficial statuses can have a down side, and harmful states can have a "good part", even if small. Same goes for skills. Of course I have some "purely good" and "purely bad", like stat boosting/lowering states.
Anyway, I hope this contributes to the topic,
Orochii Zouveleki
PD.: BTW, I'm such a troll. My Silence status raises magic by a lot. Same goes for my physical disabling, which raises atk. x'D. Anyway, just for the lulz. And actually raising magic makes them more resistant to magic. The other one though, only helps if you have a countering skill... whose aren't affected by disabling statuses.