Yes, Acumen is the most instantly effective attribute. Try this: Conquer a province whose title has a bonus to Acumen. View the province, take note of the income (post-siege, you won't get any income during a siege of course). Now drop the title onto a unit. Note his acumen goes up. Then check the province again--the income has increased!

I have so far held out for a general with 4 or greater in Acumen before giving a title. The income is phenomenal. Acumen = gold as governor.