Hi Paul....the list of amps given by DT is very comprehensive in the sub £1k bracket,and you will find that the market in that range is currently dominated by Chinese amps.
Most of these(like the Icon,Shanling,Consonance etc) are attracting very good reviews,and actually have very decent construction standards internally,with nice wire routing,and point-to-point wiring.
The currently available new valves are also of better quality than a few years ago,and sound quality has if anything improved,although NOS(or New Old Stock...original and expensive) tubes are often better,and can be considered as an upgrade after any purchase.
They do,as DT also notes,have very different sound qualities,with EL34s often sounding smoother and warmer,and the KTs having a more defined sound if that's the right word.
Don't be put of by the assumed cost of KT66s or KT88s,as the new production valves from companies like Chelmer Valve and Golden Dragon are not stunningly expensive,and can be had for the same price as premium EL34s.
I've owned the following:
Tube Technology Genesis 100W monoblocs
Lumley ST70
Quad IIs
And currently have a pair of World Audio 300Bs...your comments about the tubes for those are right....very expensive at approx £120 per tube,but the sound quality is another level again.
Reliability of all of the amps I've had has been excellent,with only the expected tube changes at suitable intervals,and you can expect small signal valves to last for up to 10 000 hrs in some cases,and output tubes will vary according to how hard they are loaded,but several thousand hours should not be unreasonable.
You may wish to look at
www.worldaudiodesign.com for a valve related bulletin board,and Zerogain may be of some use also.
As with any such place,you will find some very opiniated stuff,and the best way you will have of deciding is to listen to as many of these as possible in your own home....one good tip is to feel the weight....much of the expense,and quality of low frequency output etc in a valve amp is in the output transformers.
The coupling capacitors,reservoir capacitors and other componentry also make a huge difference,but dont expect Black Gates etc at this price level!