Would you say the same thing about playing chess, with the goal to reach a certain ELO rating?

I'd say the same thing I'd say to David Gerard, which is that deliberately trying to attain a certain improvement in skills is much closer to work than fun, and is 'deliberate practice' of the sort so valuable in other areas (pace Ericsson), and to be encouraged. If you're reading hard literature and entering words you don't know or striking quotes into Mnemosyne, that's more appropriate for this page than just reading Discworld or something.