You get roughly 670 Alex per VD run with a seal. Alex sells for 600,000 per stack on Asura. You can get 6 stacks per VD run, = 3,600,000 gil per VD run.
So just letting you know before you spend 5m/clear if you're not after gears.
I have to go through this like every other month. A VD clear is worth about 5~5.5m You forgot the gallantry value. (4500 per run) ((depending what's in gallantry for the month)) 4500/15 = an extra 300 alex = 5.4m per run.
Even at 8m it's value, IF you still need things from total hallmarks.