Value of Desk?

It appears you have a simplified mahogany secretary desk, which probably would be classified as MCM. I cannot provide any more information as the crown does not show in your picture and that is part of the information on age.
I'm not sure where your description of a 'drop leaf desk' comes from, as I cannot see any sign of a 'drop leaf'.

I believe your desk is a good example of the saying; old furniture can just be old furniture, even if it has a good brand name.

Your pictures only show that your desk is in a need of a complete overhaul, and that would be an expensive undertaking.

For anyone to properly provide any type of value information, you would have to provide several good pictures: Pictures of full front of desk completely uncluttered (nothing in or around the desk), clean top of desk, side of desk, back of desk.
In the present surroundings, it would be impossible for anyone to provide help with an answer to your question.
Heavy furniture is usually advertised as 'local pick up only' due to the high cost of shipping.
The market in your area would determine the final value whether you list your desk in its present condition or if it is refinished.
My personal opinion:
I live in mid-Florida and in my area, I would say $25-$35 would be top dollar for your desk.

The only way to know for sure is to clean it up, take good pictures, and list it for sale. Always start a sale at a higher price as you can always lower the price if necessary.