How does the KE aluminum exhaust hold up in salt water? Are they lined at all? What about airgap intakes?

I run fresh water 75% of the time, but don't want to throw money away by buying parts that aren't going to last.

I've been running 2 sets for close to 10 years in brackish chesepeake bay water and have zero issue with corrosion. Where I launch the boat is near 100% fresh water though so the KEs get a good flush after each use out is salty water. I think they will work great for you if you flush them well after use in salt.

They will last a lot longer than cast iron in salt.

If that is true, then great! same story with the intake? I thought saltwater and aluminum didnt jive?

Same story as Blue Thunder ... flush them and you'll be fine.
I ran the air gaps for a couple seasons with no issues .

Salt is hard on anything but in my opinion it lasts longer than cast iron. I rebuilt an engine on a 9 year old Jet-Ski once always run in salt, but flushed. All of the exhaust is aluminum there was no corrosion anywhere. I lost a Mercury cast iron riser at four years on my boat, have had Imco aluminum for two years and so far they look great inside.