So like, back in the old days (aka when I did VCE), specialist 1/2 didn't exist. There was General Mathematics Advanced 1/2, which everyone treated as specialist 1/2, but there wasn't a specialist 1/2 - and so VCAA designed the course in such a way that you could study specialist 3/4 without doing a 1/2 subject for it. The problem is, everybody treated GMA 1/2 as spec 1/2, so big bad VCAA decided that wasn't on - and designed a specialist 1/2 subject. The kicker? They didn't change specialist 3/4 at all - and to this day, it remains as a subject that's designed to be picked up at 3/4
So like, yeah, you can definitely pick up specialist 3/4 without doing 1/2. As for is it worth not picking it up if you do really well in further - entirely up to you. It is very common feedback that people have more time than they know what to do with only studying 4 subjects, and specialist comes with a nice scaling boost, so there is that to consider. If you think one of the your subjects might suffer if you study specialist, then it might not be worth it since only 2 of methods, further, and spec can count in your primary 4. But, if you think you can study it and the only subject that might suffer is spec anyway, then tbh you have nothing to lose and only things to gain if you take spec.