If you have an 8-9 day cruise from LA to Hawaii with 2 days each way you could hit 3-4 ports. Just look at cruises from New York to the Caribbean.
There is always research into reducing the resistance of a hull cutting through the water, the real reason being to go the same speed with less fuel, but you could use the same research to go faster with the same amount of fuel you're using now. It would take several years but it is possible to build a high speed cruise ship. I don't think you could have a very large one though. There might also be a problem with higher speeds amplifying motions experienced at sea (just like driving faster over a bumpy road amplifies what you feel from the bumps). The biggest problem would be finding someone to invest the money into the research and construction.
Past Cruises (all except one from NYC)
Carnival Triumph to Canada: August 1999
Carnival Victory to Canada: July 2000
Celebrity Zenith to Bermuda: July 2001 AND July 2002
Celebrity Galaxy to Caribbean (from Baltimore): July 2003
Voyager of the Seas to Caribbean: July 2004
Crown Princess to Caribbean: July 2006
Carnival Victory to Canada: August 2007
Carnival Miracle to Caribbean: May 2008
Staten Island Ferry, I mean what else in NYC is free?