To keep the feeling of nostalgia current, you can try to have a regular, or semi-regular, portion of your sessions involve a story or scene from the distant past.
Ideally, this would be something which the players, with their knowledge of the worlds' history (whether through background stories, or through participation in the world creation) would be able to understand, while their characters do not. Examples include finding holographic recordings of battles, or of family scenes, or any of the day to day life that is no longer around.
Depending on the situation, you can tune this. For example, some of the scenes could be played out out-of-character, allowing you to point out the connections with history, if your players aren't that familiar with the history yet. Alternatively, if the players are intimately involved in the history, the scenes or descriptions could be something that you build into the actual game play. Maybe the characters discover a device that they won't be able to actually use - beyond getting it to play a broken recording (maybe the device is an instruction manual for a non-existent tool, or a school book, or equivalent). A children's school-book might contain lessons that a player today can understand (QED?), but the character won't find at all relevant.
You can also try to create this kind of juxtaposition by showing modern tools being mis-used. A children's toy being used as an alarm bell, an airplane's fuselage being retro-fitted and used for a truck, an old hovercraft having shoddy wooden wheels attached to it and being pulled by draft's animals are all good examples. Again, these can play into your session - the devices might still be functional if repaired, or maybe they're functional to a point, where the players find an advanced piece of technology is completely missing.