I'll never sell any Infinity IRS speakers, unless I find a bigger/better set to upgrade to. [Ultimate dream: IRS Vs]. I'd keep them all, except I have no room for more speakers that big. I don't plan to sell any ESS speakers with the "Great" Heil AMT units, because I want to experiment with an open-baffle line array of those AMTs (maybe three or five or more in a slightly concave column per side) when and if I eventually get enough of them.
I think all my other supposed "keeper" speakers may all eventually be up for sale, but only when something better comes in the door. For example, right now I have AR-2ax and AR-4x speakers. From what I've heard, AR-3as are better-sounding. IF so, when I get a pair of AR-3as I might get rid of one of the others.
Speaking of AR-3as, I saw a pair this week in a shop, but the price was too high. I'll keep looking in the cheaper wholesale places for a more affordable pair. Ditto for two pair (an "instant stack" if I bought them both!) of NS-1000Ms I saw, although I might still break down one day and pay retail for a pair of them. They might actually be worth it.
If I lived in a house with a basement or garage, or othewise had enough storage space to keep them all, I'd keep all the better-sounding speakers I find. I'd probably end up eventually joining the ranks of the "certified" collectors with 50 pairs or more. Fortunately or unfortunately, that is not an option in the apartment where I live now, so most of my speakers are "at risk" for being sold sooner or later.
UPDATE (almost a year later): I no longer feel any need for collecting 50 or more speakers, even if I should have the room. However, I would always like to keep a sampling of the best ones... maybe 20 pairs, if there are that many really, really good ones that I like that much. I could almost as easily be satisfied with only 3 or 4 VERY GOOD ones, these days. I want great sound, not just good sound, and I don't want clutter. Finally learned this lesson "the hard way"". LOL.