Is it possible to spin up a new droplet from a snapshot where the new droplet is lower spec than the droplet that generated the snapshot (assuming that file sizes are within the storage limits of the new droplet)
As long as the disk size of the snapshot is equal to or less than the size of the Droplet you're trying to restore it to, you can definitely restore it.
If, for example, your snapshot is 40GB, you'd have to choose a Droplet with at least 40GB of storage available. So you wouldn't be able to restore to a 20GB Droplet, but could restore to a 60GB, 80GB, etc.
CPU and RAM doesn't matter when restoring as those are not hard limits and they are more flexible.
It is advisable to first create a droplet with a minimum size i.e. 512MB and then scale as required. However for any reason if a user need to scale-down, you will either have to physically migrate from one server to another or restore from backup or "maybe" spin a new droplet with additional block storage with a total minimum of the hard-disk capacity of your present (bigger) droplet.