1. The usage of global vs regular attributes should NOT be decided on performance, because it doesn't matter to start with. Use global attributes for variables that must persist across scenes and have a meaning in the game as a whole.
2. Global attributes are as good as regular attributes when it comes to performance and memory management. Do NOT even care about such details.
3. Global attributes are as reliable as regular attributes. (Where did that smartphone thing come from?)
4. "Blue" attributes do not "affect" actors only. These are defined at the behavior level, for both Actors and Scenes.
5. Unless you have strong reasons to believe global attributes are impacting your game negatively, which is *very* unlikely, do NOT even think about these details.
6. Using [do every X seconds] does NOT increases performance "automagically".
Many objects in a game need regular updates. Critical objects like bullets and controls benefit from as many updates as they can, while non-critical objects like a waving flag or other decorations need to be updated only once in a while.
The less there is to be done a single step/frame, the better the game performs.