I was in a similar position in regards to picking music for vce in year 10. I'd played and done the class from 7-10 (tbh I wasn't very good, and I'm still not very good

), I opted not to choose it in lieu of further maths. Anecdotally, a lot of my friends kept doing music and for many of them it sucked all the fun out of it; others thrived in the more structured and theoretical setting.
Like you said, only you can decide for you. A couple for things to consider:
- The crazy (or so I've been told) workload. Do you think you can put enough time into music? ofc the benefit is usually the time you put in is almost always proportional to better results.
- You get to further develop a neat skill (or set of skills).
- Is music theory interesting? As far as I'm aware it's a pretty big part of the course so hopefully it doesn't bore you to death
- Would what you pick instead be more interesting?
As for suggestions for a replacement: Further maths would be easy to pick up because you already do methods. History/Humanities classes are fun (classics represent

), but they're also a lot of work to do well in and not offered everywhere.
When considering a new class, take into consideration three things: What will get you into your course, what you think is interesting, and what you think you will do well in. Priority is in that order; don't do something you don't like because it scales, or because you'll smash it. VCE is more than a numbers game, it's the next two years of your life. Don't make it more terrible than it has to be

.