Lighter in some cases, arguably absorbs some road buzz (depends on the seat post how well it will dampen road buzz) which is a bonus on an aluminium frame and most importantly it often looks better!
My 1st upgrade on your bike angelsolofish would be some nice gel cork bar tape, it will help with your hands. You could also look at some of the gel systems to go under tape. Personally I think they are a bit of a rip off and I would make my own using the old bar tape. I recently tried this, I cut 4 strips from the tape I was removing, one for each of the drops, and one for each of the tops, stuck them on along the length of the bar where my hands rest then taped over it with the new tape, cant see where it is as I wrap tightly and its nice and comfy.
You will get many miles on that bike before needing to upgrade anything significant - tyre upgrades are always worthwhile from stock cheap tyres (better puncture resistance, better grip, lighter) but the actual wheel, wait until the wheels are borked then upgrade them. I had a close look at a viking on saturday (singlespeed only), looked like a bloody good bike for the money.
I can understand your concern re the brakes as no-one wants to be hurtling along at 40mph and then find the brakes dont work right, but maybe yours just need a bit of adjustment. Setup makes a lot of difference.