The trouble with most kinds of gamification, whether to encourage IDing or observing or whatever, is that they tend to incentivise quantity over quality. I agree with iNat’s stance on not introducing such features in general.
That said, I do sometimes feel it might be nice if there were occasional emails/notifications to put your own iNat uages in the context of wider iNat usage. These might say something like “congratulations on posting your 100th observation this month; this puts you in the top 2% most active users in your country” or “thanks for adding 1,000 IDs of Lepidoptera so far this year, making you the 7th most active identifier of this taxon during that period” or “great job for adding the first ever observation of xxx to the site!”. Unlike publicly displayed badges that reflect your community ‘status’ on the site, I suspect such private messages would not have the same downsides, yet would still give some encouragement by making users feel appreciated and giving them a rough idea of how their depth of iNat usage compares to others’.