You can run the drain for the tub and the shower into the same line. Check code to see how big the line would have to be to accomodate a shower and a tub, you might be able to get away with a 2" line for both the tub and shower. I think a nice big, well-designed bathroom would be better than two small bathrooms. And as far as resale value, how long are you going to live in this house? Build what you want. Why live with two small bathrooms you don't like? Also, could you add a 1/2 bath to make up for losing one of the small baths.