Seems to me that the owl is actually quite a good building. I'm at the end of Chapter 10, so here is how it breaks down for me:
Chapter 10:
1 level 25 workshop =32,180 supplies per day at a total cost of 41.62 squares
1 level 25 residence = 1,820 pop at a total cost of 17.6 squares.
1 level 19 T3 boosted manufactory = 11,520 goods per day at a total cost of 115.11 squares.
(Note: This assumes 1 9hr/10 1hr productions from workshops, 1 9hr/4 3hr from manufactories, using Lava Codexes to provide the culture, and fully upgraded roads. I know 1 9hr/10 1hr isn't common, but it's how I try to run my productions so those are the numbers I use. I chose Lava Codexes as the culture estimate because they're easily craftable).
A fully evolved Ch. 10 owl will provide 987 pop, 1953 culture, 29,400 supplies, and 7,140 t3 boosted goods, at a cost of 18 squares. It will also provide 9,240 mana, but for the sake of this analysis I'll leave that out for now.
That means it's worth roughly 0.91 workshops (37.87 squares), 0.54 residences (9.5 squares), and 0.62 T3 manufactories (71.34 squares). It's also worth 0.98 Lava Codexes (3.92 squares).
So, the fully evolved owl in Ch. 10 is worth 37.87 + 9.5 + 71.34 + 3.92 = 122.63 squares. Subtract the squares it costs (18) and you have a building that is saving you 104.63 squares.
And that's without even factoring in the mana production. I'd say that's a pretty worthwhile building to add into your city, even if the feeding effect isn't worth the cost of pet food.