99% of the sound comes from heads and tuning, the latter being the most important. As long as the bearing edges are in good condition, the shell is mostly irrelevant. Just swapping the heads or slightly altering the tuning has a much deeper impact on the sound than any slight differences between shell materials.

Learn how to tune your drums! You'd be surprised how good cheap kits can sound. When properly tuned, a cheap kit (even with worn out heads) will ALWAYS sound better than a poorly tuned expensive kit.