Of course no upgrades on VA domestic. VA's own elites don't get complimentary upgrades, except four domestic segments per year (IIRC), and then only from full fare economy. Domestic business usually flies mostly empty, even though it's only eight seats on most aircraft.

The main benefit (a biggie) for DL Gold/Plat/Diamond is access to VA's very nice domestic lounges, including on domestic itineraries.