[84LX89GT]

tires will wear out within 30k miles....it all depends on the treadwear rating on the sidewall of the tire. it also depends on your driving and how much you use the gas pedal.
an aluminum driveshaft won't change your ride quality at all. The idea behind an aluminum driveshaft is less rotating mass for your engine to drive.....there's alot more things i'd do before installing an aluminum driveshaft.
rear upper and lower control arms are an awesome investment, they make mustangs handle so much better and get rid of the "tail wag" you get if you steer back on forth while driving (that shows how much the rubber bushings deflect). Upper and lower control arms will keep the back of the car under control and will get rid of sloppy handling if you're taking a hard corner.
also, if you get a higher speed rated 16" tire (something with a stiffer sidewall) your car will also handle much better and be more responsive....but the tradeoff is tirewear. the stickier the tire, the less mileage you'll get out of it. You could get the 17" GT wheels (i'd stick with factory made wheels, they always have the right offset and the quality is much better than alot of aftermarket), they handle really well.....but the tradeoff with that is you need a smaller, stiffer sidewall tire, handles way better - but it'll catch every rut in the road so you have to pay attention while driving. My cobra with 17" wheels goes all over the road when there is ruts.
I don't know everything, but i worked on fords for 4.5 years and was a ford senior master technician, so i like to think i know a thing or two.