The temple that Sanjou-no-kata is interred at is apparently noted for its cherry blossoms. This bumps it marginally higher on the list, given that we will be there at cherry blossom season.
Suiseki-ji (where Shingen was born) looks like it is straightforward enough to get to (bus to Sekisui-ji from JR Koufu station), but might take a while. It's also on the Kai 108 pilgrimage. I would love to start this pilgrimage at temple 1, but it looks like all the cool stuff is up in the 60's.
Ah! But temple #1 is Kai Zenkou-ji. This is already on the must-see list -- preferably for the next trip.
Going to sleep now.