Here are some of the differences between the GLS550 and the GLS63AMG. These things are standard on the AMG, pricing for GLS550:
- Panoramic Roof: $1090
- Heated 2nd row seats $600
- Driver assist package: $1375
- Active curve system: $2900
Probably overlooked a few small things, then some body changes, the mentioned suspension and stuff like leather seats which don't seem to be comparable 1:1 but considering the upgrade option on the S550 are $4200 one gets an idea.
I'd say you get at least 10k worth of additional options on the AMG Model without even considering the performance and hand build engine.