ᐅ Is it worthwhile to replace windows with double-glazed units?

Hello everyone.

I took over my parents’ house in 2017.

The original house dates back to 1935.
The entire house was completely renovated in 1994. At the same time, an extension was added and insulated according to the insulation standards of that time.
In the new part of the building, Meranti wood windows with double-glazed panes were installed in 1994.

In 2017, I replaced all the windows in the original building with new double-glazed windows.

Now I am considering whether to replace all the remaining wooden windows installed in 1994 with new uPVC windows.

The windows still look really good in terms of material and show no damage. One window does not close completely tight, but it also hasn’t been adjusted in 20 years.

I have had four companies inspect the windows. Some say they should definitely be replaced, but one company said the windows are still in good condition and only need maintenance. That one window, if properly adjusted, would close tightly again.
They also mentioned that if I replace all the windows, the amount I would save on energy costs might only pay off after about 25 years.

The estimated costs are around 12,000 euros.

Can anyone share any advice on this?

I would appreciate any tips. I’m attaching some pictures.

If the windows don’t bother you, otherwise I would keep them in place until they need to be replaced….