Re: Make "Remember last dir..." be a global setting?
No. But you can set it as a default for new sessions:
https://winscp.net/eng/docs/ui_login#defaults
And you can mass-modify existing sessions:
https://winscp.net/eng/docs/commandline#batchsettings
https://winscp.net/eng/docs/ui_login#defaults
And you can mass-modify existing sessions:
https://winscp.net/eng/docs/commandline#batchsettings