Whenever I go shooting, I always have the flash mounted. I have a 5600 HSD.. while more expensive, it's really useful for nature/wildlife and the like.
You might not necessarily need KMs flagship flash, although I can't imagine going anywhere without any kind of flash. This is just me though. I like to stick to 100-200 ISO and use fill-in flash rather than boosting up the ISO to 400 or 800.
My advice? If you don't think you need a flash for now, don't buy one. Experiment with the equipment you have for a while. If you then decide that you really do require a flash, go for it.
One can easily spend a small fortune on photographic equipment even as a hobbyist.
If you think you can afford it without the cost leaving a dent in your wallet for a while, then the question doesn't even arise... I'd say buy it.