I'm usually not, but occasionally I find it a necessity.
Two examples:
1. I own an original of the Sparks LP No. 1 In Heaven, but ended up buying a reissue to play because my original is almost unlistenably sibilant
2. I own an original of Robert Pollard's Not In My Airforce, but bought the reissue for two reasons: a) retire my original copy, and b) the reissue follows the tracklisting that Pollard originally intended for release.
In this case, if you already own Abbey Road, of which there is no shortage of copies, then I get why you might pass.
I personally am waiting for the day when there is a reissue of Low's I Could Live In Hope because it's terribly out of print, very expensive to acquire even second-hand, and I'm curious to see what another issuing would improve upon (if it does).