Interesting development

@millercarbon  While your post explains some of the rise in value, it doesn't totally explain the considerable rise in value of the reissues, some of which I mention in my OP. Remember, some of these will be available again ( after repress) at pricing that is at the original retail on some of the usual retailer sites. Is it because folk have to have the album now...and cannot bear to wait for any amount of time?? Or is it something else?

Look at the demographic that spends lots of money on vinyl records.

I grew up with vinyl and I experienced all of its problems, so I am a young member of the baby boomer generation that likes CDs and downloaded digital music. 

Although my son is not an audiophile (yet), he and many of his generation made a great deal of money as entrepreneurs. They are buying vinyl in droves and others are buying incredible digital systems. Companies such as MSB Technologies are catering to this new crop of Silicon Valley millionaires for digital ($84K DAC?) and this generation of vinyl-lovers are grabbing all of the content that they can. It is an artificially-inflated market and the suppliers' profit by offering a limited product, keeping subsequent prices high, even of reissues.  

If a seller at ebay raises the price on collectible and sells then other sellers will follow as long the demand remains the same. You can also compare selling value at Discogs. Only one seller with these recordings? Monopoly. HQ pressings even some repressings are way too expensive, same goes with SACD's. I can understand the high prices on out of production SACD's and original releases on LP,  but reissues? I always skip. G

Many years ago, Mobile Fidelity had a retail outlet in Sebastapol, CA. We visited and purchased many favorites at $13.99 each. A few years ago, I sold them to a used record store dealer for $50 each. He was thrilled to get them, and I was thrilled to have sold them. I recently got back into vinyl and regret selling them, but the profit helps ease the pain.

About twenty years ago, I found and bought a still-sealed Mobile Fidelity copy of Rickie Lee Jones for $6 in a used record store. I saw it recently advertised here for $250. Now that’s inflation, or is it just supply and demand?

I don't think it's really new, but the prices do continue to climb.  It is supply and demand.  The "reissues" you mentioned are (mostly) high quality, numbered limited editions.  Some are not so popular and if they are still readily available they will sell at MSRP.  If they sold out within days or weeks of their release, good luck finding one at its original MSRP. 

Same thing happens with Record Stored Day releases.  If there are only 2,000 copies of something popular, you'll see them at double their price within hours of them going on sale.  Go look at prices for the RSD 2020 Black Friday version of Let It Bleed.