For me it was a no brainer - had a look at the std spec and left with the feeling that it was stripped out. Got in a high spec a couple of weeks later and all the missing stuff was there.
You may not "need" the extras, but for me it makes it a nicer place to be.
-17" wheels: nicer design than the std spec IN MY OPINION
-Bigger front disks
-Bigger and vented rear disks and calipers
-Cluster with white rev counter and digital speedometer. Analogue speedometer is not the easiest to read quickly.
-Programmable shift light & buzzer
-Proper alcantara/leather seats
-Heated seats: don't need
-Bi-xenon headlights are superb
-Auto headlights: nice to have
-LED daytime running lights completes the look
-Passive keyless entry with stop/start. Love this!
-Cruise control: already explained above
-Dual zone auto climate control: adds to the "cockpit" look & feel
-Various leather trim around the center console a big improvement over the plastic in the std spec
There are some other differences as well but the above are the most notable. I have posted this before but those options would set you back around R70-R80k if it was an Audi/BMW/Merc so the price difference between std & high really does make it a no brainer in my opinion. As for the weight argument, it's negligible.