There isn't a cruise line yet that offers much of a benefit to the lowest tier. In all of them you have to move up into the higher tiers to get anything of any value. But then again, since it only takes one cruise to get into the lowest tier, that is to be expected. Airlines don't offer a free flight after only one flight. Hotels don't offer a free night after only one night. Car rental companies don't offer a free day after only one rental. I've got platinum credit cards. What do these cards offer that is different from a standard credit card or a gold credit card?
The only perk that I know of from Carnival as a gold member is that the crew is supposed to say welcome back. So far that has happened to me once (not one cruise - one time) and I've been on five Carnival cruises (though to be fair, the second cruise was before the gold & platinum cards).
Royal Caribbean made a mistake by making Diamond their top tier after only ten cruises. Many made this in only three years by taking weekend cruises (a total of 30 days at sea). I've got 21 days at sea with NCL and I've only been on two cruises with NCL. I have 31 days at sea with Royal Caribbean and I've only taken five cruises with Royal Caribbean.
Realizing its mistake, Royal Caribbean was forced to add a new top tier, called Diamond Plus. And to get to Diamond Plus after having made Diamond requires more cruise credits than it took to get to Diamond from the beginning (Diamond is 10 cruise credits and it takes 14 more to get to Diamond Plus).
Carnival has made the same mistake with its Platinum being the highest level after only ten cruises. The result, when I was in a suite in May 2004, I walked up to the priority boarding line at around 1:30pm and was the only one in line. The next cruise, in April 2006, when I also had "priority boarding" half the ship was in the same line as I was. There was no "priority".
The first tier, which should cover cruises two through five should be something with very little extra. The next tier, which should cover cruises six through ten, should offer a little bit extra. The next tier, which should cover cruises ten through twenty, is the first tier that should start to offer something with some real value. The final tier, which should cover cruises over twenty (with something else special at 25, 50, 75 & 100) is the one that should offer something that is special.
Otherwise it dilutes the value of the top tiers. For example, I was in a suite on the Freedom of the Seas. I wasn't treated any better than anyone else and I spent $12,000 for the cabin. The next two cruises with Royal Caribbean I was in an ocean view and I was treated like someone special. Now why should I book a suite costing $1,700 per night when I get treated better in an ocean view costing $240 per night?
The same with the tiers. Why bother offering the tiers if after the first cruise you are already getting something special? There is nothing to look forward to. If you want the top tiers to feel special, then the top tiers have to offer something that is special when compared to the other tiers. The result, I have no desire to book a suite on Royal Caribbean again unless I need the extra room. In my experience it offered nothing of any value beyond the size of the room. Now on NCL, you get treated like a king or queen when in a suite. Even on Carnival, where the suites are really just bigger cabins (the only perk is priority embarkation), I felt like I was treated better than on Royal Caribbean when I was in the Royal Family Suite.
I don't understand where the idea came from that someone should be treated special because they came back a second time. Loyal customers should first prove they are really loyal before being treated like someone special.