As GASsers, we can always make a case for buying it, whatever it may be that particular day. I'm in a similar situation right now, and the logic I'm using is that if it's a sound that I've always loved, and ultimately want to make, I find a way to move something else to get it. In my present case, it happens to be a Hammond M3. It's a trade deal, so I get a couple of things going out the door as the M3 is coming in. I have my wife's support on this one - well, sort of. It's going to be a tight fit here, but it matches the furniture, and the sound of a real tonewheel organ is one that I've always dug even though I don't play. I intend to remedy that to some extent, much as I did with guitar, merely because I wanted to make that sound. Plus the added mojo of having a Hammond in the living room.
Re the Sunn rig... I've played through a Concert bass on several occasions, and while it's a cool rig - certainly not one I would turn my nose up at - it's tone is not one I would say has been rattling around in my head for decades. I've turned down FREE stuff because I knew, ultimately, that it would just be another chore at some level.
