I like some of the ideas in this thread.
+1 to the idea of HQ having its down Dar - no reason for it not to.
+1 to having massive Ack at the HQ - you should be flying through hellish puffy as soon as you hit the dar ring - again, no reason for it not to be defended to the utmost.
+1 to the idea of HQ being a strat / groups of buildings that have to be destroyed to take it down a percentage - I would suggest that the % down of the HQ affects the refresh rate of the dar bars like we did in the BoB in FSO. Instead of having the dar bars refresh instantly, put a 1 to 5 minute lag in the dar bar refresh tied to the percentage that HQ is down. When HQ is 100% down, the Dar Bars vanish, but regular local dot dar from airfields stays up regardless.