I have maybe 300 records. Historically I've only been a sporadic purchaser of LPs: in high school, most of the records I bought at the time were not available on cassette at the time, and CDs were still kind of an exotic luxury back then. Over the past few years, I've switched to buying vinyl exclusively since many new titles come with free digital downloads of the album.
I don't think I have too many killer rarities in my LP collection: just a lot of old (and new) records I love to play. Maybe Tortoise's Rhythms, Resolutions & Clusters or some old Stereolab 7"s might be of most interest to the collectors, but I've got my old Joy Division 12"s, old Beatles and Pink Floyd and classical albums inherited from my parents, an original pressing of Radiohead's OK Computer, Smiths LPs that have been out of print for many years (though Rough Trade / Rhino are finally re-issuing them shortly), some gorgeous Red House Painters LPs that are long out of print and worth waaaay too much money on eBay.
I do try to keep a leash on the size of my collection; don't know what I'll do when it outgrows the bookshelf, and heaven help me when it's time to move. I'd much rather have quality over quantity.