The way I've always seen it is that Morocco's ability is much more useful early game. I'm actually playing a game as Morocco right now and at 50BC I was making 86gpt in a Golden Age which went down to 70gpt when the Golden Age finished. No other civ gets even close to that from what I've seen previously. At the early stages of the game, where you're only producing 15 - 20 culture per turn, those extra 2 or 3 culture points are equal to 10% - 15% of your overall culture so it's actually a bigger boost than most people think.
Portugal, to me, is much more focused on the mid-late game as that's where it really starts shining. At the early stages of the game, your city won't have grown all that much so the unique resources may not add up to all that much. They might add an extra 2 or 3gpt to the trade, but lack the culture that Morocco gives, and other civs have no reason to trade with you over anyone else. Plus, take into consideration the caravansary compared to the harbour and when they come into play.
Of course, as the game progresses, Morocco's ability stagnates while Portugal's increases meaning that by the industrial area, Portugal's ability should be shining above that of Morocco's, but for me personally, I've already established a very nice economy by that time of the game anyway, no matter what civ I'm playing. The early game is where I usually struggle for cash and Morocco's ability really helps with it, I mean I managed to buy 3 universities the turn I finished researching Education (I think it was around the 50BC I mentioned before) because I was getting 80gpt! That's a huge science boost thanks to the early extra gold.