Another consideration is that the Multisensor 6 can be hardwired with USB power so that it provides instantaneous measurements rather than only reporting when a sufficient change has occurred.
Creating a virtual thermostat is also possible with Nest using the Nest Manager.
I’ve been using Nest Manager for a few months now, and it works really well. Nest Manager also allows the integration of Nest Protect CO and fire detection with SmartThings.
Focusing the temperature to a room that is occupied would be better than tuning the house to an average home temperature. This is one of the integrated features of the Ecobee3, and part of why it became so popular. I haven’t tried to programatically replicate this functionality in SmartThings, but it should be possible.