A few issues with this season, among everybody else's complaints.
I've heard the Laginas several times now refer to the "real treasure" not being gold or monetary but the story or the information they discover about the island's history. I think it is intentional in setting up the viewers for a final dead end, i.e. no actual or tangible teasure found at the end of this season. We all must realize this series is not necessarily presented in a chronological order. Some of the scenes we see in an earlier episode may have been shot after later episodes, maybe even after the finale. The editors/producer piece it together to try to make as compelling a story as possible, whether by hook or by crook. One of these "precursor" scenes involved the guys digging in the "old dump" on Nolan's land. Drayton found the hinges and immediately suggested they could be from a chest. Marty's reaction was pretty much rolling his eyes and unexcited.
The issue with the cross is that I think it will be the most important "find" of the season and they want to withhold confirmation until the finale so they can milk the interest as long as possible. Because it is really the only interesting thing going on in the whole 2nd half of the season. Could be planted, could be insignificant. Not sure I care anymore.
Probably the only thing that keeps me tuning in is the clip in the season 5 trailer where Marty says "Not only did we find the money pit, the money pit is real." Though based on how misleading a lot of these previews are, he could be referring to something completely different. Like "a money pit is a hole in the ground you throw money into and it took us 5 seasons to finally admit it".
Though ratings are still really high for this series, I agree that the new confederate gold series is probably intended to pick up the audience from COOI when it ends, possibly in two weeks.