It's worth it if you enjoy tinkering and you are happy to use the exercise as an opportunity to learn more about your instrument. You will hopefully gain an understanding of the electronics, how to solder, how it all goes together, how to set it up to suit you.
You might even end up with a very playable instrument.
I recently upgraded a cheapest of the cheap squier affinity p bass that turned out really well and is now a pleasure to play. There's a thread about it in the Build diaries section if you are interested.
You may well turn a profit, you may not but ultimately it's worth it for the experience, assuming you are not a complete disaster area around tools/soldering irons etc