So in the end I went to Kanako's Soup Curry Shop, which I've walked past countless times (one of my favourite cafes is in the same building) but never eaten at.
Kanako's started here I think, and although this is their only store in Sapporo they also have a branch in Hakodate and two in Sendai. That kind of 'soup curry outreach' is highly commendable. The quicker soup curry spreads properly outside Hokkaido, the better chance I have of not having to go cold turkey when I travel. I kid. A little.
I just had their standard vegetable curry and it was nice. They use a spice-blend from Sri Lanka apparently, and the soup curry flavour was good, but I wouldn't rave about the place. The ingredients too (Hokkaido sourced) were good but not sensational. I think I probably need to try one of their recommended dishes to see the best of the place of course, but overall I'd say this place is worth going to if you want soup curry but you don't really mind not being blown away. Spice-wise they have a scale that goes to 100 and that gets spicy around 20 apparently. I had a 25 and for me that was a pretty mid-range spiciness.
Oh! Y'know what I've been meaning to start posting addresses and opening hours for these places, since that's the kind of thing might be seen to be somewhat useful right?
Kanako no Soup Curry-ya san (Kanako's Soup Curry Shop)
Sapporo, Odori, South 1 West 1
Open Weekdays 11am-3pm and 5pm-9pm (9pm last order)
Open Weekends 11am-9pm (9pm last order)
...and it looks like they don't have a holiday!
It's nicely located really near the TV tower, and I've stuck it on the map. Hopefully soon I'll be able to check out one of the soup curry places that people love and that I haven't had a chance to get to!