When i had a bad line fault that lasted a year i was told that turning off my router at night would not cause the DLM to raise my SNR or lower my sync, After my line was fixed i was called by someone from BT and told to keep my line on 24/7 for the first 10 days i think it was.
After that i could return to turning it off every night when i went to sleep.
He informed me that the dlm would not consider this as a fault if i was only doing it at night and not every time i switched of my pc.
I have been doing this since march and i still have an IP profile of 5mb and snr has never moved from 6.
So if you ask me from my own experience, turning off the router once a day before you goto sleep has no effect on your SNR or IP profile.
Ps i am now on the new profile system so no longer get 1,1.5,2,2.5 and so on, think its 5.3mb or something stupid like that for my profile now