"Is it 'worth it' to replace the plaster with a more modern (?) smoother plaster, since this probably (?) fits better with the windows?
I already find the change of the windows to be inconsistent with the style of the house.
It is a risk to first install windows that are less fitting to the house and then choose the plaster afterwards.
I think that one should not modernize the exterior of the "old" house.
That is indeed a high art.
You have a beautiful house with somewhat rustic shapes, proportions, and an "80s bay window." You are not turning it into a look that is currently preferred – be glad, because your house is definitely more timeless than some of the currently highly sought-after city villas.
Therefore, I would work with the house and not against it. On the facade, you can play with a combination of not too fine wood and plaster to connect natural material and plaster color. The plaster color can then also be a real color, a statement, instead of a bland gray that does not really suit the house style. The canopy over the front door and the balcony railing can remain wooden but get somewhat straighter shapes and more harmonious proportions. The house can also tolerate vegetation – for example, a wisteria.
For something truly modern: move instead of bending.