I think the most comprehensive and cost effective solution will be separate home security & home automation solutions.
Here's an interesting blog I discovered today and made me think of this thread.
https://diysecurityguy.wordpress.com/2015/09/08/review-envisalink-evl-3/
So I was looking more into this, but unfortunately it doesn't appear compatible with rental-friendly alarm systems. The supported DSC models all appear to need to be hardwired.
I thought the Vista had to be hard wired, but there's just wiring the alarm panel itself (just a utility-like box with a circuit board inside, also intended to have a certain type of battery in there as well) and the keypad/control pad. From there you can add a wireless receiver to then utilize wireless security devices.
The price of monitoring coverage is still something to consider. But at least a module like the Envisalink would get me IP-based remote control, and I could add a Vista Automation Module to add a Z-Wave controller.
I'm back to researching the price for Alarm Relay for more limited but cell-based monitoring.
But I am also very much eyeing the Abode and Scout packages. Not sure how the Honeywell Vista package would add up, but Abode, while a little pricey to configure good coverage, is primed for automation and paying annually it's $20/month. Which, for cell monitoring, seems to be the lowest rate (not the only provider with that rate, but I can't seem to find anything lower). And with Abode, I wouldn't have to hack together a remote access system.
Scout is a close-second to Abode, but it doesn't seem to truly offer Zigbee support, it's mostly confined to IFTTT and some support like Amazon Alexa and Nest... and I'm still trying to wrap my head around how IFTTT works when you aren't home and want to manage connected gear remotely (does it work like that?).