hey
id say Wiz is a must for any serious SnG player and imo its defo worth the money they ask for it. The question is whether you really need it so early in your career. Dont get me wrong, i think it can help a lot on any stakes, but im pretty sure that you can be a solid winner on the low stakes without using Wiz for your analysis (which doesn't mean that you dont have to work on your game in other ways obv).
I bought Wiz when i moved from 6$ to 12$ (back on FT) and before that was able to get a decent ROI without it. I just used other ways of working on my (late) game:
- practice with the ICM Trainer A LOT!!!
- marking hands while playing and putting them into holdemresources calc after the session (its a bit of a pain in the ass but with a bit of practice it doesnt take that much time)
So thats what i would suggest, especially that now holdemresources have their Beta calc which allows you to adjust ranges for you opponents if you think theyre not playing according to Nash (which is basically the main reason why you use SnGWiz).
to sum up - buy Wiz as quickly as you think you can afford it, but before that happens dont worry, you can still work on your late game in other ways, even if sometimes its gonna take you a bit more time than if you had Wiz.
hope that clears it up a bit for you, if you have any more questions feel free to ask 
cheers
