I leave my Line 3SE in standby when not in use and have for over 5 years without problems. I seem to recall that the owners manual indicates that if you aren't going to use it for 3-4 days then you may want to power down.
Leaving the heaters powered is not the primary wear mechanisim for tubes. The main cause of tube wear comes from the stripping of electrons off the cathode and depositing them on the plate. This happens when high voltage is applied during normal operation. Small signal tubes can last on the order of 10K hours because the currents during operation are low compared to power tubes in amps.
The real advantage to leaving the unit in standby is the elimniation of thermal shock at turn-on. As you have found, the unit takes a few hours to reach thermal equalibrium which does affect the sound, and it's just easier on the equipment.
As for not leaving the house with the electroics powered, that's a personal decision. But remember, there's typically a lot of equipment that stays powered when you're gone such as clocks, refrigerators, timers, alarms, etc. I'd be guessing, but your MF A5 CD might not really be fully powered down when "off" but in standby. The pre is fused so if there's a problem you should be covered.
A different POV but you decide.
