Having had both - the 1000 is different to the 800. Its more open sounding (not just an EQ thing) and a little more responsive. Its not a world away though.
I too have compared the GT to a couple of tube power amps - and they did add some extra life its true. I also compared it to a valve power section of a regular head - that also added life but a lot of EQ colouration as well. As Ive said before though - the "light bulb" moment for me was when I then compared a real amp to the AFX with the various power options - the AFX/Matrix was closest. While the options utilizing valve power section sounded more alive, and indeed better - they were further away from the real amp, so in that sense less accurate.
Ultimately - you choose a solution that works for you, based on your own priorities - be that authenticity, life, feel, weight, size, power, volume etc etc etc - then you rock out
Id also add - after recently going to two big concerts involving acts that have been around the block for 30+ years. The FOH sound was so indistinct, you couldn't tell if it was produced by a £3+ amp rig with £3k+ boutique pedals, an AFX/SS power amp, or indeed a broken SS transistor radio with a 1.5" driver. Really - what goes out front bears no resemblance to what you hear on stage however you do things (even FRFR and direct - it SOOOOO depends on the environment as well), so when getting "choosy" over relatively small differences in sound/feel/EQ etc, it is really only to pamper our own inner sense of "great".