Congrats on the 5-0!
Echoing @ajfirecracker, I've found 1-3 Ichorids to be very strong in the maindeck. The biggest value in my mind is having another way to trigger Prized Amalgam. Adding just one Ichorid increases the probability of having a way to trigger Amalgam by 25%.
The down-side of Ichorid is that it is relatively inflexible across the match--it's much better Game 1 than in Games 2-3. I think in general that cards supporting only half of the plan in a hybrid deck need an especially-high cost to benefit ratio for consideration. I think that the first Ichorid meets that criteria comfortably, but I'm not 100% sold on additional copies, as the returns diminish quickly (at least regarding Amalgam triggers; +20%, +17%, and +14% for adding each Ichorid beyond the first).
I haven't had time to play in any leagues in weeks, but I did play in five leagues with 2-3 Ichorids and 1-2 Golgari Thug and went 18-7. A small sample size, but the Ichorids felt smooth.
Like you, I also have developed mixed feelings about Leyline of Sanctity. It's so good at ensuring lockpieces stick around against Outcome, does great things against Oath, and deals with targeted hate like Ravenous Trap and Tomord's crypt. Consequently, it synergizes with both halves of the deck, but it also doesn't help win the game and does so little on its own.
As I side-note-- I have adored your Stax lists since I started playing Vintage in the early 2000s. It's cool to see you back!