How much should I care about prepared statements for simple queries?
The difference is negligible much of the time. You'll see significant benefits if:


There are lots of joins or lots of predicates; or
The query contains long IN lists or similar large data elements


In general, unless it's a "hot" code path where you really hammer a particular query   I wouldn't make much effort optimising to focus on re-usable prepared statements.

(You should still parameterise your SQL rather than substituting parameters directly into the text, and people often confuse that with prepraed statements, but you seem to understand the difference.)