If you were hoping that iOS 8's ability to hide your device ID from nearby WiFi networks would render you invisible to nosy hotspot operators, you'll want to dial back your expectations a bit.
Apple's hardware address randomization only kicks in under a very narrow set of circumstances. You not only have to put your device to sleep and turn off location services, you have to turn off cellular data as well -- in short, your iPhone has to become a paperweight.
The only way to avoid giving out your hardware's real ID is to stop using your hardware.
The risk of revealing anything truly personal is relatively slim, but you're not going to be happy if you were hoping to go incognito around public WiFi access points.