I actually DOWNgraded by getting a 75 to add to my 150 (combo). I agree with other users that the 150 is frankly too loud for anything other than full band rehearsals or gigs. Even then as my many patches tend to be saved with high volume (to achieve a fuller tone) I find as do other posters that I need the Master Volume at 9 o'clock and any tiny increase risks blasting my bandmates away - handle with care! I also cannot play it in the house as, even with no patch and turned right down, the 2x12s are just too loud.
So I got a 75, would have bought even smaller, but of course the 75 is the smallest Spider iv which shares all the same tones and amp models as the 150, so I needed this to be able to fully copy all my patches across when using the 75 at home and in rehearsals where I can't face lugging the big 'un around.
Incidentally, that is another factor to consider when upgrading....those bigger amps are damn heavy.