Don't expect too much from it.
I don't know about Alamy, but on Dreamstime multiple of my photos made it into their 'Editor's Choice' collection in the past and some of them haven't sold even once and I sell far more on Dreamstime than I do on Alamy.
You can see it as a nice confirmation that someone out there appreciated your pictures, but as far as promotion goes - I don't even know where to find the AlamyPOTM gallery linked from their main page, so I doubt all that many customers will see it?