I have been watching this thread for a while now, and I think I have heard enough from both sides now to interject my hunch here.
After hearing about the primary documents concerning the missing payroll (by the way, SOMEONE needs to track these documents down!), I think that the story could very well have been greatly exaggerated. Now, here's what that means.
1. Goldenrule--I would believe you are right to think that a heist of the reported amount of gold should appear somewhere in a newspaper or enough reputable primary documents to vouch for its truth in some part. If this story is greatly exaggerated (and we've only heard about a "payroll" from a primary document so far on this post!), then there was a smaller cache stolen--certainly not the amount of vast amount of gold reported in the paper 150 years later. This story from a primary document may have laid the basis for the exaggerated story about wagonloads of gold. And in that case, there is no telling whether that payroll was ever recovered by the theives or not.
2. Goldenrule--I agree with you that whomever pursues this tale should want to see these found coins first. I would look through the newspaper articles and find the name and info on whoever found the last one of these and politely ask to see the coin or a photo of it. That would settle some questions quickly, and the last one was supposedly recovered only 20 years ago or so. Get on it, folks! The thing that is perplexing about all of this, Goldenrule, is that the first coin was supposedly found in the stream the 40's--before the newspaper article about the treasure was printed, and before the Bates' even knew about such a story . So we can't write this story off as entirely fabrication at this point! This last fact does allow us at least the possibility that the story has some truth to it.
3. I, personally, am perplexed about the continued reference to "Washington Dollars" in the info on this post. Now, of course, we have Washington Dollars minted our country, but never has there ever been a gold "Washington Dollar." After doing some poking around...if these were indeed French coins (regardless of how many of them there originally were--and I suspect a greatly smaller number than what the account says), it is possible that the first person (in the 40's) to find one of the said coins looked at the date of it (late 18th century) and saw the portrait on the front and ASSUMED that the portrait was of Washington himself. After all, as you'll see in the photo there is nothing on the coin that identifies it as specifically French. The inscriptions consist entirely of abbreviations in Latin:

But it is still troubling that something would be identified as a "dollar" if it was gold. I would think the accounts of found coins would be much more likely to say something about these coins being gold if indeed they were even gold in the first place. Hence, some other contemporaneous coins--close in size to the U.S. silver dollar and likewise made of silver: First, the French ecu:

Second, the 8 reales:

All of these international currencies could have been used for payroll purposes, and any of them could have been likewise mistaken by a novice.
4. Tommy--I agree with you that the pursuit of this, even if it turns up dead ends, could put you onto some other great sites and leads. So I don't feel that it is a waste of time. (There might be a payroll still stashed somewhere rather than wagon loads of gold). But I would think that talking to the people who found the coins in the creek is first priority. One could speculate about this treasure endlessly, but actually laying eyes on said coins would greatly help this tale's reliability.
Regards,
Buckleboy