How much thermostat "range" in oven temperature is too much? I recently renovated my kitchen and have a new Bosch wall oven. I've noticed many baking recipes that used to be reliable are no longer so. I have a ThermoWorks ChefAlarm and calibrated my oven according to the procedure on their website. The accuracy of the oven is pretty good - usually only 5-8 degrees lower than the display says. But the temperature swings are surprising: they're +/- 30 degrees. So if I set my oven for 350, the temperature ranges back and forth from 320 to 380 over time.

I've never checked the range on previous ovens so I can't say if this is normal. It seems to me to likely be a problem, especially when a cookie might only be in the oven for 10-12 minutes. Does anyone know? And a follow on: I'm tempted to reach out to Bosch customer service to see if there is a field modification to change this behavior. Anyone know if that's realistic?
This is fully normal. Ovens are not stable, temperature-wise, and I have frequently seen such large amplitudes in temperature. Of course, it is much nicer if your oven can hold a constant temperature, that's why some people will accept the expense of an Aga. But in principle, baking recipes can handle that. Note that from a historical point of view, people used ovens with solid fuel, which had much larger temperature amplitudes and no temperature display, and their baking goods were still tasty. Ovens are not temperature-accurate, and recipes are robust for that.  

As for the recipes which are no longer reliable, the most likely explanation is that your old oven was also inaccurate, but in a different pattern. Another possibility would be a different mix of radiant, convective and conductive heat, which means that the same recipe in the same pan can require a different time. In general, a recipe which specifies time is reliable for a specific combination of pan, oven and amount. If you bake until ready instead of waiting for a time given in the recipe, the problem disappears.