I know what I previously said was somewhat of a blanket statement, but the ironic thing I've seen is that throughout multiple tube amp threads there always seems to be some consensus on the best 2-3 sets of tubes to put in that amp, and everybody strides for them.
I've tried tube rolling before with 3 sets of different tubes, and the results weren't different enough for me to consider it a worthwhile investment. Not only did I not find it worthwhile, but I ended up spending as much money in the tubes as I did the amp.
If I want a big change, I get a new pair of headphones or amp. If I want a fine-tuned sound, I EQ my headphones. If I want the 'best' sound an amp can provide, I allow the manufacturer to build the amp around the particular set of tubes they've chosen and produce amazing results. That seems to be the case with the 120 dollar Vali and its tubes.