Howdy and welcome to Airforums.com, mnpaul2102! This is the place to find the answer to most any Airstream question.
Here's my thoughts on your question regarding the value of your original furniture.
I do not think that you would be able to get much cash for them, since most people that have a trailer like yours would be, like you, thinking of upgrading the interior, not keeping the status quo.
However, BEFORE you do anything drastic, including selling them, consider holding on to them for at least until you have finished building your new interior. There could be no better pattern or template to work from than those pieces that were originally custom-fitted for your trailer.
The other point to keep in mind is that the original bath fixtures can be made to look remarkably new if they are professionally painted...
All the best luck for your project, and how about posting us some "Before" photos of your rig as it sits now?
By the way, some parts, in particular the refrigerator, can be worth money, if they are in good operating condition. All the more reason to post photos, good clear ones, especially of the interior.
Finally, a good place to sell any of those parts you do decide to move out is the Classifieds section of our site. In fact, there are usually some parts on there, and you might be able to get an idea of values by having a look 'round.
Up top, just below the "S" in "FORUMS", is the entrance door. Use the same user and password as you created to get on here.
If it's to be, it's up to me.