Any lens you've got is perfect right up to the point where you understand why it sucks.
It sounds like you're using the lens now. If that's the case, then you're in the best possible position to evaluate whether it's working well for you or not. There's no question there are better lenses available, but your experience with the lens should tell you whether you're running into specific limitations that you want to spend money to solve, if that makes sense. Do you need a different focal length range, or a faster aperture, or a sharper lens? All these things are available -- though you might find yourself purchasing multiple lenses in order to get them. That's the classic "what lens should I get" question, and you want your personal experience to play a big part in that decision, if at all possible.
The "feel" of the lens, as you pointed out, is part of what we like or don't like sometimes, too. Tools with good ergonomics help us work better, you know? So if you find the light plastic-y feel getting in the way of producing photos, then that's absolutely a factor to consider as well.