It's alot of money to spend - I think for most folk a different set of pipes and a change of filter would be plenty. To be honest, the one I test rode a few years back sounded nice even with the standard pipes. Similar but different to my W650 if that makes sense. High performance bikes are wasted on me! Lol.
I noticed if you went for the big bore kit (450cc-ish) from Hitchcocks for the Himalayan and added all the bits they recommend you're up towards £2000.
Regards
Tony