Did you book a specific cabin or a guarantee?
How many are in your party?
Did you ask for an upsell to a higher class cabin? I'm pretty sure if you were willing to part with that $100 credit plus a little more, you could move into an oceanview or balcony and cruise your orignally scheduled week.
Your travel agent is probably correct too. But 4 months out from your cruise is much to early to make deals.
Expecting any cruise line to hand over a higher class cabin for nothing is asking too much, even if the original problem or fault is theirs.
By being just a little more flexible and loose with your cash, you'd probably be cruising on the POAm in an oceanview or balcony cabin on May 20. If you're going to be inflexible, NCL will too. All the inside cabins for this ship are selling out anyways.
You booked an inside cabin, and they're offering you an inside cabin a week later.
More than just the May 20 POAm cruises have sold out inside cabins.
Here's today Travelocity report for May 2006
2006 Departure Date(s): May 6, 13, 20, 27
Inside Sold Out
Luckily you found out about this prior to Final Payment Date, and it is your right to cancel if you so choose. You can always sail Hawaii at another time.