I'd like to pass this thought around like a bag of chips so no licking your fingers please.
I'm getting more and more (and more) frustrated with debating whether or not to use a Skill Point only to still~ fail the test by 1. The way the mechanic is set up is understandable in that you may or may not succeed even with the help. The question of being able to choose to use luck is moot. Both versions allow you to choose if you use Luck. What I'd like is for you to consider the impact of being able to add luck after the fact (as is done in some puzzle solving).
For example, an Investigator rolls against his dexterity missing the result by 2. His luck is 3 and decides to use one skill point making his check a success by 1. Even though this would be a small edit in the rules it will vastly change the outcome. I support with the following reasons….
1-The new Luck ruling would be known. All players know going in that the Luck can be used when wanted and adjust accordingly.
2-The Investigator player still needs to decide when and if they use any Skill points to gain the Luck value.
3-Even with this powerful ability, a check is not guaranteed.
4-Several abilities at the Keepers disposal can still cause a check to fail.
5-As an Investigator you gain a choice and lose frustration.
6-The keeper normally has the advantage. This helps close that gap.
7-Luck will feel like luck!
This is by no means a new topic but worth revisiting. I do not think that the current ruling represents luck all that well. Luck is something you discover after the fact and recognize it. You don't go in buying a lotto ticket knowing you will win, you buy a ticked and are surprised when you do win.