"creating" a duplex through purchasing two semi-attached units

[Jon Fults]

I'm under contract right now for a small 3bd/2ba rental property which is a semi-attached home as it shares a wall with one other unit. I've done a little of investigative work and think I may have a good shot at making an offer off-market to the owner of the adjoined unit (who is also using the property as a rental) that I could pursue once this deal is closed. 

Before I go down that path, I'm curious if there is any big benefits for organically "creating" a duplex here outside of scalability (or any disadvantages as well). E.g., at exit would selling a duplex fetch a higher price than a single unit? (I feel like usually I see it the other way around -- I see discounts offered if a buyer takes down both properties). Perhaps some benefit in lending terms if I finance the whole unit as a duplex as opposed to two single family units?  Any other pros or cons I'm missing?