Pen costs HKD 3600 and up (circa HKD 8000 for the nicer suites that are worth getting) so it is a different price point. Of course it is nicer! As you might expect from one of the 10 best hotels in the world.

The Sheraton Towers is actually quite good -- much nicer than the Sheraton part of the same building (and run mostly like a separate hotel). Not really much to upgrade to in the Towers, except the view. At the pricing you quote it is the clear winner -- by far. I used to alternate stays between the Pen and the Towers, finding it to be that good (price/performance).

Staying on the Island is a big mistake for a tourist. It is great for business, but as a tourist staying in Kowloon is far better. You chose well in what hotels to consider and I think the Towers will suit you. Don't forget to make use of the most excellent Towers concierges, who can arrange anything for you. Very useful in Hong Kong and they are better connected than most other hotel concierges.