Re: 1905 Queen Anne on the Michigan/Indiana border -- open or closed cell foam?
I'd lean towards open cell. It won't trap moisture, so you won't dramatically change the characteristics of the existing structure.
What were you insulating again? I spray foamed my the roof deck in my attic right after I moved in and was pretty happy with my first electric bill. My attic never get over the upper 80's with only 6" of open cell... so around R20. I still need to remove the existing cellulose on the attic floor joists.
You'er still looking at a 10-15 year payback realistically.
1925 Two-Story Stucco Beaux Arts Neoclassical