I haven’t tried using two resistors in parallel as a gridstopper. I’ll put that on my list for investigation, but it’s a long list.
I wasn't thinking grid stoppers, I try not to ever use grid stoppers, now a days.
But,as one example I know of, where the paralleled and closely matched Rs shine is for an Ra and a Rk, both positions of the same tube. I parallel in 90% of my build locations, on the vacuum tube Ra and Rk in particular. It gives two equal paths, is more dynamic, better sounding, quieter, and plain ole FUN to hear !! The very best place to try this initially is on the Plate Resistor, of an early input stage. Bump it up on your priority list !! :-)
The MFA manufacturers ( of a friend's Luminescences, plural ) were using 2 Watt Cornings on something like a 12AX7, and went to parallel Cornings, matched very closely, several decades ago.