So I've been playing for about a year and a half, and I focus on metal. I'm at the point where I can play semi-competently and am wondering about a good amp. I have a roland cube 60 now, which from what I can tell is a pretty decent amp, especially for the music I play. I've never played through a tube though. Is the sound difference monumental?

Tubes seem to be a lot more expensive, so what would be a logical next step for a good amp for someone of my ability?

Also, if it makes any difference, my main guitar is a custom agile ghost III with an EMG 81/85 combo.
Its pretty big difference your cube insnt using the EMGS much, tubes have more dynamics sound more "Fluid" and get louder and smoother.

Whats your price range on a new amp?
Schecter C-1 Hellraiser
Ibanez EX 470 (1991)

Peavey 6505 combo
Vox Valvetronix AD15VT
Danville 1X12 Cab
Kustom 12w tube

Dunlop Crybaby
DOD overdrive(YJM)
Boss Ns-2
Dod 250 Overdrive