I had pretty much the same requirements in my environment where I only needed certain interfaces to trigger an email alert when Utilization above "X".
Not sure if the most efficient way of doing it, but effective enough to accomplish what I wanted.
I created different Custom Properties and just so that i knew their significance, I named them "Interface Util over "x" threshold" I mention "x" threshold because I have 3 sets of them.
I placed the interfaces I was interested in under that Custom Property.
On the advance Alerts I specified the custom property to be Interface "Util over "x" threshold" = True
I have an advance alert with custom properties like this one for our ISP links set at 70%
I have another alert like this for our Core links.
So far they have worked for me
Hope that helps