12au7's will last thousands of hours, and they are cheap - don't worry about it. get the best you can find and enjoy them. life is too short to worry about it otherwise. Vintage 845s can last as long or longer than chinese, I think. I have probably 1000+ hours on a pair of Cetrons right now and they are as strong as day 1. Vintage 845s were guaranteed for military use (read: extreme, at times) at usually 1000 hours. Often times of course they ran far longer than that. several thousand hours would not be unheard of. I have some 1006-845 amps, I think they run @ 900v or so around 85ma - not overly hard on the tubes. if the 1009s' run them similarly, I'd expect quite a long number of hours from a pair of vintage ones.
The difference with vintage 845s, while perhaps subtle (to some), is definitely there. Value/worth depends on every individual's situation. To me, they are worth it. With some work, they can be found for relatively reasonable money. (read: about 1/2 or less than what tubeworld.com wants for them).
thanks
-Ed