I agree, keep writing whether good or bad, and never with just the intent of getting a freebie. The only way they can improve on things is to know what they need to improve. Also, think about those that went out of the way to make your vacation more enjoyable. I wouldn't let the fact that I no longer get a freebie keep me from acknowledging them.
As for pricing and the discontinuation of the fuel supplement, I don't think they are losing anything. I had been watching a couple different sailings and found that once the fuel charge was discontinued, the fare increased by a proportionate amount. This may not have been the case on all sailings but it was on those I was watching - all 7 day Caribbean. I ended up booking the Legend out of Tampa for Mar '09.
NCL Sun, Oasis OTS, Navigator OTS, Legend, Fascination, Emerald, Glory, Mariner OTS x 2, Sovereign OTS, Celebration, Miracle x 2, Pride, Fantasy