Well, my 5c on this topic ... I apply every 4 months for a better rate, and they just say no and give a reason or 2.
But if you want to move to get ebucks, if the rules change in the banks favour and you get less, you will not be happy. Example, year on year customers earn less and less on rewards.
I would say, if a bank offer you a great rate, with an awesome package, go for it.
I know friends who bank at investec or RMB ... (That banks offer more than the lower end banks), if that makes sense
How do you apply for a lower home loan rate at FNB?