At room temperatures, the +32 is significant, at cooking temperatures, who's oven is even accurate to 16/32 degrees? It depends on if knowing the "right" answer is more important than knowing an answer that will get you to what you want e.g., tasty muffins rather than charcoal briquettes :)
C->F: multiply by 2, then add 30
F->C: subtract 30, then divide by 2.