Hi, I'd just like to say that since you're doing Methods in Year 11, I think this helps a significant amount for Spesh in Year 12. Quite a few of my friends and I felt that Spesh followed on from Methods quite well (particularly in the calculus section and to some extent in the graphs section.)
To answer your question, I personally believe Spesh will get you a better score, provided you are committed enough to see it through the whole year. At the risk of sounding overly dramatic, it honestly does take some effort to not 'drop the ball' for a subject. Now, I'm not only talking about completely letting everything slide, but letting everything slide just enough to jeopardise your chances of getting a really good score (seeing as one of your aims appears to be Medicine).
So from a purely marks-oriented perspective, I think Spesh can well prove favourable. I genuinely hope you do enjoy it though, (because that honestly helps an incredible amount) and that you really enjoy learning what you do, both now and hopefully into the future. There's absolutely nothing wrong with studying what you love, and it will show.
Just my two cents.