I think he would have been able to conquer Dacia, but Parthia is another thing. He would be successful in the battlefield, but he would run with the same logistical problems as Trajan. I don't really think much would be changed to be honest. You could say an earlier Dacia could serve as a bulwark against later Gothic expansion, but against this, despite Hispania and Gaul being conquered even earlier as well, they were two of the first provinces to permanently fall, the Romans never recovering except only portions of them after the 5th century (and never recovering any after the 7th). Of course, they also lost Italy including Rome to the Goths despite this being the old heart of the empire.
There was actually an offer made by the king of Armenia, to the Roman general and governor of Syria, Crassus, the Armenian king offered to allow Crassus’ army to march through Armenian territory and strike at the heart of the Parthian homeland, the king also offered to give Crassus 30,000 infantry and 16,000 cavalry. Crassus refused and he, along with his son, his six legions and his Gallic auxiliaries, perished at Carrhae. But what if Caesar was given the same offer, and he accepts. Now, Caesar’ goal would never be to conquer Parthia, it would most likely be to annex Mesopotamia, and give some border regions to please the Armenians, so he would march through Armenia, defeat a Parthian army or two, and force them to sue for peace, and he would receive Mesopotamia, which would probably become a sister province to Syria. According to our ancient sources, Caesar’ planned invasion would’ve included 80 legions, plus auxiliaries, but that’s just too many men for just one campaign, so his army would most likely include 10 or at max 20 legions, which at ful strength would be 50,000 to 100,000 men, which is somewhat plausible, let’s also give him 10,000 Auxiliaries from across the provinces, such as Gallic and Germanic cavalry and light infantry, Cretan archers, and maybe even Namibian cavalry, ad the 46,000 Armenian infantry and cavalry, and that gives him a total of 156,000 troops at max, though the number would vary. Mesopotamia, if annexed, would become an extremely rich province, and would allow Rome access to the lucrative Indian Ocean trade, the tax revenue generated from tariffs on this trade would probably be enough to finance Rome, Mesopotamia would basically fulfill the same role as Egypt did in our timeline (speaking of which, Egypt would probably remain an independent ally of Rome, instead of a province).