Typically, I will pull the number 1 target with shield lob - flash and circle of scorn as soon as they all get to me - full halone combo on number 1 target (with spirits within used during combo) - flash again. Then, if there are only two mobs, I either use savage blade on the first mob and halone on the second. If there are 3 mobs, I will savage one non-number 1 target and halone the other. After this I MAY flash at some point, but usually I don't need to. I just watch all three threat bars and use savage blades and halones as necessary while using circle of scorn and spirits whenever they are up (typically, I will savage the extra mobs and halone the first one unless the first one has plenty of threat, in which case I will halone an extra mob as well).
So, generally I would say NO to flash spamming (I only need two in the situation above). The only time I spam flash is when multiple targets somehow get off me, or if there are small mobs to aoe (such as the beetles in WP).
I will use it on bosses for the blind, but obviously am not spamming it.
EDIT: I think new tanks rely on flash too much. I did Aurum Vale the other day as a MNK. On the second boss (the cyclops), when it did its aggro drop, the tank was running around trying to flash it (and missing due to range) instead of just using shield lob.