Not sure if these are categorized under 'additional services' but...

Premium Listings.  Sounds crazy, I haven't sold a domain using this service yet but.  Even crazier they charge something like 30% per sale.  Upside: Exposure.  If someone types your domain in to godaddy to see if it's available they will see it's available but at a premium price which you set.. Naturally with a huge commission and huge exposure you will set your premium listing prices high.  I have a tutorial on how to submit premium listings and a sample image of how your premium listing will appear in a post I did a while back: nametalent.com

Also I've picked up a few nice domains from godaddy auctions, closeouts.. Worth taking a look at once in a while IMO.

Except for private whois addon did not see the need for any additional service.

Couldn't say. Never used any of those add-ons. It's tricky enough to work your way through all that junk and make a clean exit at checkout, without bob having made an extra buck out of another victim.

I am use only Search Engine Visibility.