@Mor - You could probably call yourself an amateur aquarist even if you only kept guppies. I know it would be nice to have a decent saltwater tank, but it's good that you know your limitations.
There are too many people who think they can skip corners and end up harming the animals they put in their tanks.
And that's what I think being an aquarist is all about really. Trying to keep the animals and plants in your care as healthy and happy as possible.
This is true of a marine aquarist who works with big or rare animals, but I think it's just as true of a hobbyist who works with little fishes and snails and things. You owe it to them to keep them safe.