For one I've learned changing out your preamp tubes has more of an effect than changing your power tubes.
Wow! Just goes to show that everyone runs into different situations/circumstances.
I believe this to be absolutely true for this individual, but I have seen almost the opposite.
While changing preamp tubes did make a very noticeable difference in my Ace, the power tubes (that is, getting away from the stock str447) made a greater difference, IMHO.
Granted, in my example, we are talking the el34's, not 6l6. I have used Mesa 6l6 in my 50/50 and was happy with them.
So if you stick to the 6l6, you may be just as well off with the Mesa's. But I don't shop for 6l6 anymore since I converted my 50/50 to use el34.
All I can really tell you is you won't know until you try. Listen to input from folks here on the forum as it can give you some idea where to start, but really, when all is said and done, you are just going to have to "bite the bullet" and buy some new tubes to try.
Then, and only then, will you know what sounds good to you.
Good luck