Harsh on tubes?

If tubes are run hard (high current through the tube and/or high plate voltage) they tend to have a short life. Run them conservatively and some tubes have an incredibly long life. There are people who report that their table radios have been on for most of the day for 50 years with the original tubes.

Small signal tubes used in preamps typically last much longer than output tubes in amplifiers. But, some designs do run them hard so the tubes may last only a year in daily use. The good news is that when they go, you just have to replace the tube; there is far less chance of small signal tube failure causing damage to the component than is the case with power output tubes in an amplifier.

Whether you can live with an preamp that runs tubes hard depends on your own willingness to provide maintenance, whether you are uncomfortable with the fact that the tube and sound may be deteriorating quite quickly and you have to monitor the situation, whether the cost of retubing the preamp is reasonable to you, and whether the sound of the particular model warrants the extra cost/trouble.

Most of the tube people I've talked to say that turning off equipment prolongs the life of both tubes and the other components. It is true that, without tube rectification, the tubes are subjected to a pretty quick turn on. But, the thermal stress is NOT as great as that experienced by a light bulb, and so it is not as big a factor in tube life. With tube rectification, the rectifier fairly slowly starts to deliver current so there is even less stress to the other tubes making startup stress far less of an issue. In any case, you will be balancing two different factors that contribute to shortened life of the tube -- turn on stress and the inevitable wearing down of the filament/cathode that comes from use. Leave the amp on all the time and one increases that form of aging while decreasing the stress failure form of aging.

Also, heat is the killer of most of the other components of gear. Hot equipment shortens the life of capacitors and resistors and other components (particularly electrolytic capacitors).

If you are not sure which way to go, the manufacturer is probably the best source of information.