Yeah, your display may be reaching its final days.
There are a few things you can try though. First, connect it to another system and see if that makes a difference.
Second, try moving it to another location or or plug it into different power outlet, preferably on a different circuit.
Third try to move power, or any other kinds of cables that might be causing electrical interference away from the display. Bad shielding can occasionally make stuff like this happen.
Have you added any new appliances to your house lately? Like an air conditioner? Stuff that sucks a lot of energy? That could have an effect. You can try swapping the display's AC cord as well.
I've been battling with a 17" Trinitron I use as a secondary display on my G4 for about a month now. It's been fine for a few days, but it has a tendency to go into these spastic moments where the brightness gets so high its flushed out, or instances where it's really dim.
I rearranged some power cables and it's been fine for a while now. I'm thinking the DVI > VGA connector might just be shielded poorly. I'm still not entirely sure what's going on, or if I've solved the problem.
BTW, you might want to check if that display wasn't covered by an Apple replacement program at some point. You might be able to get it repaired for free. Are those B&W displays ADC, DVI, or VGA?