I believe so too. NOS tubes from 5-60's are generally superior in sound quality to tubes made nowadays, but they are even more expensive also because they're quite rare and limited in supply. But I have a good feeling the fuse replacement will also yield pleasantly surprising results for its measly price.
From your Headfonia article, I can see that you have a lot of experience in tube rolling. Are there some 6SL7 family of tubes (along with replaceable ones) that you'd recommend?
It's important to be careful about generalizing too much regarding old tubes.
There are fantastic old tubes (thus legendary status), equaly good (as new productions) and pretty poor ones.
I haven't had time to roll any 6SL7's thus only what I've read. Don't like giving tips that I haven't heard myself.
But... what I've been told from individuals whom ears I trust.... Tung Sol 6SL7 = Pretty neutral; Brimar CV1985 = warmer, can be a good start. Although that 300$ NOS one you bought most likely can't compete with these 40-50$-tubes.
Will update with my own findings when I start rolling.