And you hit the nail on the head with the perpetual "upgrade, lose money" cycle I'm in. I baby my gear and it never leaves my house. When I sell (and thereby lose money), everyone always says how great of shape everything is in...like new condition except I'm losing money in the process!!! Thank goodness the Axe has cured that cycle on the amp side of the house!
man do i know that cycle all too well. i'm in the same boat. problem is that i only trust myself to provide quality used gear. if i had a little more faith that the guy on the other end of the ebay transaction was more like me and in the same cycle, i could buy used stuff in perfect condition and take a much smaller hit when i sell it to fund the next toy. theoretically you look at that ebay feedback record to get that comfort level. maybe one of these days i'll wise up and do that!
i agree with the try before you buy recommendation. no doubt those focals will sound excellent and they are obviously useful beyond just powering the axe, but playing guitar with studio monitors has a different "vibe" to it than playing through guitar speakers (or larger format speakers like PA speakers). i also know that trying to evaluate something like this on a showroom floor in front of strangers watching you play is pretty far from ideal.
it's a tough call for sure. losing coin on a pristine guitar that you really like only to find that the studio monitors aren't exactly what you were looking for would be a bummer. i think your best bet is to take your axe in and listen to the floor models. also, if the guy's amp clones have effects loops, maybe he'll even let you run the axe into the return of one of those to give you a sense of how different it is to hear the axe through an actual guitar speaker. if you find that you prefer the latter, it may be a strong clue that studio monitors won't do it for you.
good luck!