There is absolutely nothing wrong in improving upon an idea aesthetically, but it should not come at the cost of sacrificing function and practicality.
Design can be art, yes. But art cannot be design. Both art and design are aesthetic, and serve to express an emotion or a story. But the key differentiating point is that design also serves a function.
There is nothing wrong at looking at a particular design and wanting to express yourself by doing it your way, or wanting to improve upon it aesthetically. Doing so doesn’t make you a bad designer, quite the opposite. But throwing out a design’s functionality in your redesign doesn’t make you a good designer. It doesn’t make you a bad designer, either. It just doesn’t make you a designer, period.
I am absolutely one of those people who says both “design is for solving problems” and “we need more creativity on the web”. Both those sentences coexist very well in my opinion. Design has always been in the context of problems and solutions, and a call for more creativity has never meant an abandonment of the subject context. Be more creative, but within the parameters of design. And one of those parameters will always be “purpose”.