There have been several posts along this line of thought, and I wouldn't be opposed to more ack being added. I don't know about the 5"ers though, but some more / varying types of ack would probably be good.
HiTech, I think, posted quite a while back about the addition of or increased lethality of ack, and it's effect on gameplay. The basic idea, if I remember correctly, is that when ack becomes overly heavy or hard to take down, then people start 'hiding' in it more, which then has a negative effect on gameplay. However, every base turning into a vulchfest after 3 cannon planes make one pass isn't exactly a good thing either, so I'd be all for some tweaking.