Any domain name will sell, at any given point in time, because a buyer desires/needs your domain.
In my opinion, the actual reason is highly irrelevant (startup, upgrading, media campaign, email, branding, sister website(s), defensive, link juice, added internet presence).
The key question is: are you investing in the types of domain names that a respectable % of end users will probably want to own down the road? (knowing that you will only shift, on average 1-3% of these per year).