Previously the feed I used for Planet Plone looked something like this:
Which resulted in a feed enclosed between feed tags like this:
My new URL now looks like this:
The new approach (ie. appending ?alt=rss) resulted in a feed with an rss tag like this:
I did not delve into what other things get changed by using '?alt=rss', but the most important outcome is that the "Planet" (Planet Plone) is now safe from the occasional updates and revisions to my blog posts.