Yeah, was thinking about that too. Out here, the coolant is expensive, though I just found the right Glysantin being blown out for 5 euros/1.5L, so I could put the savings into the thermostat, I guess to avoid having to change it out for a while. We drive very little, but we use the car heavily for our couple of vacations a year and cross-country family trips, so based on mileage, we end up doing about 8k miles a year- so thermostat might outlast the coolant, based on cycling (since we basically head to the highway and drive). I don't know- thermostats are cheap, I hope, so then I might just do it.
It seems like I'm being neurotic about this, but when it comes to fluids, we have to be really careful in Germany. It's not like the US. Here, it's basically 82 million nosy environmentalists and changing fluids at home is sort of unheard of. Fines and prison for releasing the stuff into the environment, so I have to figure out how to do it as few times as possible to minimize risks.