I agree - the vintage testers are usually fine for looking for bad faults, but don't usually run at actual amplifier voltages. Sure they can test for shorts and breaks, but they don't tell you if the tube is noisy, and the readings could be accurate to +/- 25%, *and* as mentioned are only at the tube testers voltages.
If you were serious about tube testing you'd look into something modern, but you're going to pay for it!
http://www.maximatcher.com/http://amplitrex.com/If you're set on adding something vintage, which is still pretty cool and does have some use (I have two from the 70s), here is some reading for you.
http://www.alltubetesters.com/articles/tester_guide.htm