The question you're examining (which I'd phrase as "I know what a lottery ticket is. Knowing that, do I want to buy it?") is something that I don't think falls exactly under epistemic nor instrumental rationality - I personally call it "volitive rationality", the skill of correctly analysing your utility function, which is a necessary step after you've taken your model of external reality (epistemic r.) and before you proceed to figure out which chains of future events (instrumental r.) will lead to the outcomes you want more.

I should probably try making a post about it, now that there's a Discussion section for such a not-fully-fleshed-out idea.