The nature of solid state electronics is that they tend not to die, and usually not in stages.
A broken/mashed screen - sure. You already know what a cracked LCD looks like though - and it isn't a gradual process.
What
can happen is the death of the LCD's power inverter. Depending on design of the unit, this can result in the screen still functioning (ie,. LCD matrix registers a change state in color), but the backlighting is gone. When this happens, in most designs, this means that the screen is practically unusable. In other designs, the whole frikkin thing dies, and the matrix cannot display any change states at all and the backlight is also gone. There is no debate as to usability in that event; it's not pining for the fjords - it's
snuffed it.
If you are trying to convince/justify to a wife that you need a new 24" LCD, you could suggest a lightness dimming and flicker as a sign of imminent inverter death - and then claim to have seen it
(And usually - you don't. The inverter works - or it does not.)
If you ARE getting a power flicker on your screen where it is dimming out then coming back - then yes, you have a power inverter on the brink of drowning that is somehow clawing its way back to the surface - and it's time for a new monitor.
You might want to look at your cable and connections though. Might be
that to blame more than the rare power inverter working then NOT working, then working AGAIN.