There are a couple of things you could do without a plugin, though. You could delete the entities in the first model (and purge the unused components) but leave the secens as they are. Save the results as a new file. Then copy the second model into this saved file. Presto!

If both models share stuff like background or have common parts, you could associate a layer with "version 1" and another layer with "version 2" in the same SketchUp file. Leave the things that would show in both versions on a third layer or Layer 0. Then go to each of your existing scenes and swap version 1 for version 2. Create new scenes for the version 2 views. After you've completed that, you can reorganize the scenes so all the version 1 scenes are together and all hte version 2 scenes are together.

Takes longer to write about than to do.