I personally do not see the point of 3. Qxd4 in the Smith Morra Gambit. It is no longer a gambit (unlike the main move of 3. c3) and just loses a vital tempo in the opening.
Are there any proponents of 3. Qxd4 out there, and if so what are the advantages of playing that system?
Here after 1. e4 c5 2. d4 cxd4 3. Qxd4 black managed to get a highly advantageous position by using a standard Dragon Sicilian setup. Due to the fact that white's queen moved on move #3, never mind the lost tempo after the queen was attacked and had to move a second time after 3...Nc6, it became difficult for white to setup the standard anti-Dragon dark squared bishop/queen battery with the bishop on e3 and the queen on d2.
In this particular game white's queen and dark squared bishop never quite properly coordinated and along with other positional errors, such as trading (or being compelled to trade) light squared bishops (in my experience in the Dragon white's light squared bishop tends to be more useful than black's) and not defending the queenside as well as possible white's game never really got going and black was faced with zero difficulties. And after just 17 moves white called it a day.