Absolutely keep observing common species if you like it. You never know how it is used later.
When Corona hit and the curfews started, I started observing frogs in my backyard. Every evening I went out there and photographed each individual I saw. I had my own agenda to keep me busy, wanted to see how many different individuals and how loyal to the location they were. But of course I also thought about how - if ever - those observations might be useful beyond my own entertainment. I thought maybe it might be interesting for someone looking for intraspecies variation, especially as this species is not too commonly observed with only 15 observers so far… or maybe the same questions I had in mind might be interesting for someone.
Well, those observations indeed were used for a publication, but very different then I had anticipated… someone looked into the kind of retreats frogs and toads would typically use and used thousands of iNat photos for that - rare species like the one I had observed but also super common ones (and I actually only know, because they also used one of my photos to depict one kind of retreat… so even a second way my observations were usefull). For that kind of purpose indeed more photos were better then less. Very nice, very interesting and very unexpected. Since then I really stopped worrying about how useful my data might be, as one really never can know. I observe what I want to observe… nothing more, nothing less