> Could too much thermal insulation cause the bed temperature to lower (to avoid overheating chamber temp) to the point the print no longer adheres? etc.
That would depend how much "safety" is built into the control system.
The simplest solution I've seen is taping up the edges of the enclosure where you find gaps, to prevent heat escaping.
If it's only PID-ing the bed, the ambient temperature shouldn't matter. Less work to do for the bed heater. On the nozzle, it's similar. A 40 C increase in ambient temperature isn't much compared to the 150 C+ that the control system is maintaining. Since the active parts of the printer must be capable of running at the target chamber temperature, there should be no risk unless you exceed it. The question is really, is the printer designed to operate continuously with a chamber of X C?
However... the risk would be that if it's too well insulated there isn't a good way for the system to cool quickly if it needs to, or if it somehow messes with what the control system is tuned for. On the older printers you could re-calibrate the PID loops to your specific hardware and environment. The newer 32-bit firmware seems to not require user tuning at all. Similarly with full enclosures, you might worry about the power supply or other electronics which aren't meant to be run at high ambient (maybe fine though).
You could also look at a separate solution like enclosing the printer in well-insulated chamber, and aiming to keep that outer space above ambient. That would be a good option if you're expecting a big thermal gradient to your workspace, like an unheated garage in winter.
But lots of questions really. Do you want to run at a high chamber temp? Are you running in a cold environment and having problems? Trying to save power? These are different scenarios.