Dunno i have so many boosts at this point from events i boosted everything i had (including the radioman) started another line boosted that and i still have over 30 boosts.

I'd say boost whetever you can. It's some extra stats whenever Hardcore mode hits. 

Depends on what state they are and what gunz you are using.
I assume you are using +12:
using 3.46 AA: No, you can hardly notice the different.
using KM40: You may, you will be more easier to find out the different.

Personally, i will boost them as i am using H44 now.

But i have NO BOOST (But a lot of points and credit) GET DURING LAST/ THIS EVENT. OMG. 

Theres no point unless you want a better spread. However your spread wont be great unless you classed outside the norm anyway. I boosted mine with the intent to get a better spread around 100 and saw no difference in reload and only a slight increase in accuracy with all aa gunsets.

Don't get rid of them yet.

Wait until SS6.  Maybe, just maybe, we might get our U-flak guns back.  On the other hand, I still have my U-flak gunners (L112).  I'm now using one of them on my SS5 (in place of my Chf Seaman) because my SD is already above 800.  I've learned how to dial in range and have hit some planes with the pop gun (34 degrees) too.  I've dropped CVs without wasting another torp, polished off a depth-charge-dropping FF after I surfaced.  They'll put a hurt on a FF, pretty harmless to anything else.  But you can dial in range at 45 degrees and torment CVs with HH outside their range, while you recharge and refill air. In reality, they're only good for sinking a fishing boat.  Not too many of them in Navyfield.

Also, you can super skeleton the gunner and lard up with armor and keep your speed. 

Start using them.

I'd certainly trade a support slot for the U-flak guns back.

Common sense in all SS line use main gunners and not AA.