I have this Windows problem and am looking at replacement. I understand, however, that there is a new technique which can get rid of the mist and restore effectiveness. Google and other sites give some links but there does not seem to be a definite answer of the effectiveness of the new, non-replacement, technique.
We once had it done. Two of our year old windows partly misted up between the two layers of glass. As the windows were still under guarantee we called the installers. I think they drilled a tiny hole in the plastic frame (invisible) and sucked the condensation out, then re-sealed them. I'm probably over simplifying the process, the kit looked reasonably technical. It took about half an hour and it worked fine. By the way, this was about 5 years ago so not sure if it's the 'new technique' you're referring to.
I imagine simply sucking moist air is would not be very effective for long. The air /damp got in -there after manufacture presumablyy so there must have been an imperfect seal- which if not located and remedied will allow moist air in all over. 1st., find the leak and fix it then fill the cavity with dry air or nitrogen would be the only effective in situ treatment - but the proper way would be total unit replacement.
Why don't you try a humidifier! we had a leak in the shop below our flat which resulted in our bottom landing soaking wet we couldn't even open the heavy oak front door with ease so our landlord got us a humidifier and it got loads of water out of the walls,
The windows have a partial vacuum or inert gas within the glazing. If they are misting up then the seal is broken some where. Very difficult to fix without the right gear and a new unit may be required...