Freschi on the principle of charity

Well sadly I am not much of a Berkeley scholar so I am probably not the right person to defend him. But I guess a defense would go like this: as an empiricist he holds that our access to reality is through the senses alone (this is one of the plausible intutions I have him referring to). Also (another plausible intuition) we do in fact have access to reality: if it was an open question whether our sensation even gets hold of things the way they are, then pervasive skepticism is looming. Thus, to be is to be perceived. I fear your thermometer objection would give him no trouble at all: you have to perceive the thermometer too, of course, so it is just one more thing we perceive as interacting with the rest of the perceptible world, i.e. the only world there is.

If this is roughly the line of thought you can see that Berkeley is throwing down a fundamental challenge: either give up on empiricism, embrace skepticism, or be an idealist like him. I agree the last option looks unappealing but so do the first two. You could even argue that this line of thought is among the most central in the history of modern philosophy, since Berkeley has put his finger exactly on the problem with Humean empiricism and allows us to understand why, for instance, Kant would have thought it made sense to go for transcendental idealism. Hence it is one of the best examples of your third category ("stimulating") since like, evs.

Incidentally we can I think take a lesson from this, which is that often (maybe even usually) the interest of a given philosopher or text is not actually in the conclusions that are reached. Conclusions might strike you as plausible, silly, whatever, but fundamentally that is not where the philosophy is happening. The interesting part is in seeing how the conclusion was reached, what avenues were ruled out or overlooked, what intuitions were used to motivate the argument, etc.