Metroid Trilogy might not have a lot going for it (except the collector's tin and new play controls), but I can think of one REALLY good reason why all of us should be buying it up while we can: it is discontinued.
What this means is that it is already scarce and is only going to get even more scarce as time progresses. If you have even the tiniest desire to own this game, right now is the time to get it. A year or two from now this might be selling for $200 or something, because then it will be being sold at collector's prices. So I kinda see it as an investment to just own it even if you don't plan on ever playing it.
I grabbed a copy just for that reason. It was in "like new" condition which means I can play it without depreciating its value, and then I can hold onto it for a year or two and wait for the value to skyrocket. Since Nintendo isn't making or shipping this anymore, this is pretty much inevitable.
So there you have it, that's a damned good reason to own this game. It is called "collector's edition" for a reason, and collecting is the reason why one should own it.