Approximately no one comes to the UK to look at gas holders. It's not like number of infrastructure nerds coming to look at King's Cross and St Pancras would drop if we were to remove the gas holders nearby. But yeah, convert them into park-like areas if the community wants (as they're doing at King's Cross)
People go to Paris to see a radio tower that's rather short by modern standards. Hint: Tower.
I don't think there are any gas holders that are going to become that iconic but a lot of tourism focuses on interesting infrastructure like dam's, buildings, towers, walls, bridges, etc.
