Provincial votes are going to be even more important. While I think the ANC is going to keep Gauteng, FS, Limp, NW and MPU, there are going to be interesting contests in:
WC - where the DA / ID coalition should win
NC - where the ID has a strong chance of winning (largely coloured population)
EC - Be interesting to watch, but the new party (whatever its name is) might attract strong support, with Zuma being a Zulu man.
KZN - Interesting. Zuma is a Zulu which will gain some support, however we might see a resurgence of the IFP.
In short, while you might not change national politics, your vote could go a long way in terms of the province.
For those of us in CT, this would be especially useful for service delivery, as it would mean that CT is able to do its job without having to fight the WC administration.