I'm not a buyer of sellers (aftermarket) domains. That said I do view the NP auctions from time to time and will bid/buy quite happily up to around the $50 mark. - But it has to strike a chord.
Sold a domain this week that I've held for nearly 20 years, deducting all the renewals left about a $600 profit. But that's me these days - happy to just play around with whatever I've just got left.
My lesson was 20 years and holding 2,000 domains just became a lot of hard work, (around 2007) The money side started to pale into insignificance with all the time it was taking up. Incidentally that was the same year the wife died, (and my partner in domains) So its taken me this long to extract myself. Once you build-up that portfolio, there's never a quick way out with out loss