Looking at the stations above; I took a quick gander as to which I think are ripest for redevelopment.
I looked at the land area of the station first (how big a site); I then considered whether there was strong potential for a land assembly, then whether separation distances or height limitations may impede value; and finally the exact siting in terms of desirability.
My overall take (no inside info) is that Jarvis/Richmond is target 1. It's over 20,000ft2, the adjacent properties to its east and north are short (no separation distance), and also not listed/designated structures (suitable for land assembly).
After that Richmond/Parliament has the next potential for size of land, plus likely permissible height; but it does have a large development proposal hemming it in on the north.
The site in Cabbagetown is surprisingly large, nothing to its south is designated or listed either. But I foresee issues w/getting higher than mid-rise in that location.
Wellesley/Jarvis has a heritage building to its north.
Both gas stations on Spadina are comparatively smaller lots and encumbered by heritage, and potential separation distance issues as well.