Cathedral road had plenty of run down properties on it even up until the late eighties,smashed windows, a few squats and sectioned off into shitty bedsits. There's a cardiff landlord who took advantage of the grants scheme during that period ( A bit too much) who did very well down there.
I think it was more like the 1940’s,50’s etc….my uncle was a builder and had about 30 houses in pontcanna, unfortunately he sold them off for pennies in the 70’s/80’s they’d prob be worth 20 million today.