Well, theres no disguising it!!
We've just sold our G2 listed and yes I do think it was more difficult (although strangely the price was higher than a modern house). Ours was also in the country which didnt help matters.
There isnt much of a local market, so we had a lot of viewers from London, but once there they didnt seem to have really thought through the whole "life in the country" scenario. They didnt like the low ceilings (they're not really), they didnt like the small rooms (wanted open plan), didnt like not having double glazing, found the garden too large, wanted extortionate amounts off for what was basically ongoing maintenance ( a large house so in 2 years x or y needed doing), didnt like the tractors trundling through the village, didnt like going 2 miles to the farm shop for bread/milk.
I suppose it depends who you're market is, but keep rooms light, bright uncluttered as generally this where they fall down against modern homes.
As for the windows - we were allowed magnaglaze, a thin PVC screen which temporarily fixes to the actual window frame. The National Trust uses a similar version. We didnt even have to get listed permission, just called in to see the council with pictures. Its amazing and stops all draughts.
Now I need to find myself another one in our new area!!