The CT101 looks awful compared to the nest thermostat. I don't think you are raining on a cool personal project.
I just think that designing hardware to fit within another piece of dead hardware just to achieve what can be done off the shelf for $50 is not really my idea of a fun personal project.
Plenty of cheap thermostats have good aesthetics. The $30 round Honeywell analog thermostat is a timeless design. Their $30 non-programmable digital thermostat (RTH5160) is aesthetically pleasing enough, I certainly wouldn't call it ugly. I didn't interpret the stated goal of this project to be particularly relevant to aesthetics.