I would say if you're really, really struggling with maths now and that is due to it fundamentally not being your sort of subject (that is, you've worked hard to improve, but you really just don't get it), then you're going to struggle with methods. Yr 12 moves pretty fast, and you'll have heaps of other subjects to concentrate on, many of which require quite a bit of reading and essay writing. To improve markedly in maths, you need to have lots of practice, but for that you need time. 3/4 Methods also builds remarkably on what you do in 1/2.
If, however, you are doing all right in methods, but not that great, and you haven't really worked very hard to improve, you really do have that opportunity (if you maybe put in a bit of work over the holidays). Whether it is worthwhile depends on your perspective - if you mean for your aggregate and ATAR, quite possibly not since it is so easy to drop down in methods and if it doesn't come all that naturally you may need to put in a lot of time to doing well in it. But in terms of general learning, I have a friend who didn't do methods and regretted it later, doing an arts degree to Melb - took up maths as a subject in uni. Take what you want from that! I spose my point is that methods is a pretty useful subject to have up your sleeve, if only for a more complete maths knowledge.