. . . and I guess one power-off of router (i.e. overnight) per 24hr would be a risk??
I think the usual advice is to leave the router on 24/7, and that always my own approach.
The big risk is that you currently seem to be on a BT DLM target margin of 12dB. If DLM thinks the line's unstable, it may increase that to 15dB, whereupon subsequent connections, at least for several weeks and maybe forever, will be reduced by several hundred kbps.
That said, if the choice is between voluntarily powering off at night, or an error-rate-induced connection-drop in the small hours, I'd say the former (voluntary power-off) was less likely to be perceived as instability, and so less likely to cause problems.
However, if you ever need to use the DSL unexpectedly in the small hours - say to check a train timetable or whatever - then you'll likely connect at a poor speed which will drag down your IP profile for several days afterwards.
7LM
You're beginning to get my measure . . & . . . . . do you know my wife
No, but I've been there, done that, got the T-shirt. My own partner is also a software engineer, so she ought to understand, but I still manage to surprise(/scare) her once in a while.