So, if I want to combine the yuan-ti temple idea with some of the DuckTales ideas, I need to brainstorm a bit.
The point of the sunken ship in DuckTales was to get the party interested in finding the further riches of the Valley of the Golden Sun. But the yuan-ti temple is not a golden paradise waiting to be found. It is an active temple inhabited by a cult of yuan-ti and fueled with human sacrifice.
Did some of the yuan-ti pureblood agents plant the sunken ship solely as a ruse to lure adventurers to the temple? If so, the yuan-ti would be prepared for their arrival. The party would likely be captured and have to escape. That is all well and good, but I imagined an ignorant population of yuan-ti being infiltrated by the investigating PCs, not the other way around.
If the sunken ship was not planted, how does it lead the PCs to the temple? It could be that while searching for the two halves of the map, the bearer of the second half (not the high priest of the coin) was abducted by the yuan-ti. But this implies that the ship was only recently sunk if the PCs' investigation of him lead to the temple.
Perhaps the map-bearer was headed on another adventure that passed by the area of the temple. He was trying to finance an expedition back to the Valley (or just heading to his homeland to put one together) and befell an accident. The PCs then stumble across the machinations of the yuan-ti. But this seems rather haphazard. Even if the map was subsequently found by an adventurer who was then abducted by the yuan-ti, although that is the best choice so far as it directly ties into the yuan-ti "problem" of raiding the countryside for human sacrifices.
I doubt that the yuan-ti happened to build their temple next to the Valley of the Golden Sun but it does now make some sense that they would seek out such a rich and majestic temple as one made from solid gold to welcome their god into this world.
My initial plan was to have the sunken ship contain half the map and cut out the coin priest. However, what if the coin priest was replaced by the yuan-ti. Venkatesh possesses some item or knowledge that is necessary to find the Valley of the Golden Sun. He is either using it for an alternate purpose that fits with his plans (the key to the Valley is also the key to the dimensional gate that will allow his god to enter our world) or he is planning to find and loot the Valley himself (he wants to offer up an incredible tribute to his god when he arrives and the gold of the valley is fitting).