Good idea, Mame, sensible and it sounds like it works.
We used to send color photo postcards of our featured gallery artists' work, one artist a month; I think Modern Postcards was the name of the firm we used. A good photographer could probably make her own card runs. It would take a little cogitation re picking the type face and wording on the back of the cards, and the spacing re post office needs.. but once worked out, that info would stay almost the same every month.
We had enough to do, handling a design business at the same time with making the pro quality postcards ourselves.
I think ours came in batches of 500 at the smallest. We'd give a goodly batch to the artist, as they often would have their own connections. Not cheap, when you count the postcards and the stamps. We didn't just send them willynilly, given the cost, but either to past buyers, people we knew who might become buyers, and some of the town's movers and shakers. Worth the expense over a year, I'd say yes. but some months were a 'no'. We also brought a press release and photo to the local newspaper, and sometimes that got in the edition pre the gallery openings. Once in a while we got some full writeups on the artists.
I still like gallery photos, but I don't know if galleries like ours are doing that anymore. I do get fabulous postcards from the Irvine Museum, real treasures when they show up - but they aren't there to sell paintings, only to exhibit them. In their case they are fostering continued knowledge of early california painting.