I'm not a domain professional in anyway, but I have a few domains that I have been hanging on to, and I have no idea whether some of them are worth even trying to sell or just let them go. I let a couple go recently just because I couldn't see them being worth anything and the fees to market seem relatively high. I have a combination of generic tlds and .co.uk tlds and a one dictionary word .co.uk that I paid good money for not as an investment but for my business at the time.