I'm curious as to why you need a DI for keyboards. I've never thought of using one since the signal is so hot that I've not had a problem with noise picked up on long signal runs. It's generally been more of a microphone/guitar thing. But I could very well be wrong, so I'm interested in your reasoning.
When playing through PA you should definitely use a DI.
It will convert line level to mic level which will make the sound guy's job easier, it should reduce hum from your rig, and can potentially prevent electrical faults.
A good soundie will provide you with one if you tell him in advance you require it. Nothing wrong with having your own though, drummer and guitarist in one of bands both bring their own, I let the engineer look after me.