My stack is currently at my practice space now so I can't exactly test this for myself, but I was wondering if you would get a good volume boost if you plugged one guitar into both inputs of a guitar tube amp using a patch cord splitter or some other similar device.

It seems logical to me that it would, but I'm dying to know if it works for sure.
Vantage Ghost Gibson "The Paul" copy
Fender FM-100H half-stack
Regal vintage 30W class A amp head (handcrafted in Montreal)
most amps, when they have 2 guitars plugged in, make both inputs low gain. You might have more volume, but you will have less gain.
Ibanez RG4EX1
Epiphone SG w/EMG's

Peavey Windsor Head w/ JSX Cab
MicroCube (for the sake of practice at college)

Pedals :
Fulltone Full Drive 2 Mosfet
Digitech Whammy
Dunlop Crybaby