I agree with you. The bunker and trench are good ideas. Don't get rid of them. All the things you state in their support are correct. It allows the public to interact as well as learn about being in a place like Vietnam. I definitely liked them and they helped make your whole camp realistic for me.
The bunker is something that definitely shows how we lived. When the 101st Airborne took over at our old camp, they immediately set up tents and wooden barracks and tore down everything we had left. On one of their web sites, they criticized the previous occupants (us) for living like "rats" in the bunkers. But in reality our bunkers were safer than any canvas or wooden structure they slept in, even if sandbags were piled up around them. Also, the sandbag bunkers were cool and comfortable, except for the occasional snake, lizard or other critter that might sneak in. Trenches have been around for a long time and they have their obvious important function as well--something that is known by all who served in or know about the military. Both are easy to construct and maintain and I think your reproductions were well done and appropriate.
The other suggestions we've been kicking around will provide you with ideas to make your exhibits more interesting and varied. I think you are all on the right track and will come up with a great set up for next season.
Now how about a latrine where you can burn the s--t in the 1/2 55 gallon barrels with diesel fuel? (just kidding)