Such letters are boilerplate sent to prospective dealers for the cars. Since it wasn't signed by Tucker himself the value is not as high.
I would expect there are thousands of these from across the country as dealerships in those days handled multiple vehicles with so many still existing in 1940's.
Actual value without Preston's signature I'm going to say a Tucker collector who doesn't have one might pay in the neighborhood of $50, maybe a bit less or bit more. If it were a letter actually signed by Tucker and concerned features of the car the value would be in the several hundred range. Stock certificates with his signature can be bought for $150 on ebay and a bit more at shows.
Standard ephemera is always a bit less than we think for post WW2 Automotive related.