I would be cautious about focusing on rare species or rediscoveries of lost ones in an effort to maximize the impact of one’s activities on iNat.
To start with, it requires first actually finding and correctly identifying that species, which is often a matter of luck. In some cases one may be able to use old records as a starting point to search for where a species is likely to be if it is present at all, but rare species are, well, rare, and it is reasonably likely that even intensive searching may be unsuccessful (though it is possible that one may make other notable finds while doing so).
In addition, for the documentation of a rare species to be relevant for conservation, the relevant people have to be aware of the find – i.e. they have to be looking at and using iNat records, whether on iNat or on GBIF. My experience is that this is far from universally the case. Where I live there are at least two other competing nature observation apps and various biodiversity recording schemes by both nature organizations and government bodies, which may rely on completely different methods of gathering information depending on the state or region and the type of organism in question. Where I live I have the impression that people involved in nature conservation typically either aren’t aware of iNat or they don’t take it seriously, meaning that a notable find is fairly likely to go unnoticed (and, potentially un-ID’d) by anyone who might be able to recognize its value unless it happens to be seen by a taxon specialist who finds it relevant for a publication.
So closing the circle – making sure that records are getting to local people off iNat who can use them – is an important part of the equation.