I love my No Stripe. I used to read how much lower the gain was on Black/No Stripe Mark IIIs and pretty much wrote them off for my needs...until I played a few. Yes, they have less gain than a Blue and even a Red Stripe, but they have plenty of gain for any genre you want to play. I certainly wouldn’t pass on one, or feel the need to mod it to Red/Blue specs.
As far as the differences between a No/Black Stripe/Dot and the other Mark IIIs, other than the gain differences, I’d say that the Black Stripe has a different feel to them. The Black Stripes I’ve played seem to be a little more touch sensitive and react more dynamically to the way you play, but it’s slight. It’s not really as dramatic as comparing a Mark to a Rectifier, but it was a difference.
Yeah, the used market is just straight up stupid right now. Has been for a year. It’ll be interesting to see what prices do when all the COVID upstarts start selling their gear off.