“ if I boot a vm it's going to be nearly unusable (can't install packages) because it's going to spend the first 30 minutes doing a full upgrade” - wouldn’t be an issue if you install from the newest image. Also if your cloud provider is so crappy that it actually takes 30 minutes to apply a few updates maybe find a new one.
I'm sorry but this is neither on point nor a good advice.
I can't be bothered making a new packer image each time a new ubuntu image is up. And people to use USB keys to make their friend and family try Ubuntu (or you know, as a backup).
Also, because even if your point is wrong, you're kinda right: you can disable autoupdate in the seed file or during install. And also, minimal image are a good idea/good practice and won't ever take 30 minute even if your image is really old.
