i have a $100 yamaha nylon i bought a few months ago, which is the only other guitar i have.
i remember reading an interview w/ Brent Mason where he said a cheap nylon can sound very close to an expensive nylon. That its a smaller quality gap than steel string. there is still a difference, but I think the basic theory is pretty much dead on.
I used to have a taylor anniversary limited (XXX i think?) and a Martin Thomas Humphreys classical. I regret selling that one, its probably really hard to find nowadays. they had this cool neck extension that let the entire top vibrate independently. Both of those guitars had amazing intonation, i think thats the biggest gain with expensive guitars.
after I got RA in my hands a few years ago I walked away from guitar completely.
I've been on meds for a while and my hands are better now, so ideally I should get back to it, but i've forgotten most of what I used to know.
its difficult to know if I'll ever really get back into it permanently, so Ive been reluctant to buy any new guitars. Its a shame, because its only now that I can actually afford the real stuff, not the beater guitars that I currently have.