Yes Brian, most travelers have the same problem. I'll be paying US$10 per GB but only for the data I actually use, so of course I have to be careful as well. That seems a lot, but it is about the same as we normally pay for prepaid data in many countries anyway.
However, we don't pay for bandwidth we use when logged in to WiFi networks in campsites, Home Depot and as I found out yesterday, even Walmart, so all our big stuff gets done then. The settings are such that if we are using the Google Fi as our modem, no updates and attachments and photo uploads are transferred and the system waits until we are on an "unmetered" service (meaning unmetered for us) As for the smart phone, that is even smarter and individual apps can be ordered not to use my paid service. Roaming itself is not an issue as the Google data rates are the same all over the world and the phone rates only vary by a few cents as well.
If you ever get bored, just buy a smart phone and then you can spend hours and hours going through the thousands of apps and trying out all the interesting ones and customising your phone to there and back, and you will finally realise why everyone else in the world just can't stop messing around with the darn things. Just have to watch the data figures though - nearly 12GB just to set up the phone