I believe that you get +2 for each trigger.
Fate of the Void says - "When an enemy under your Warlock's Curse is reduced to 0 hit points or fewer, you gain a +1 bonus to any single d20 roll you make during your next turn."
Improved Fate of the Void - "Your Fate of the Void grants an additional +1 bonus to the d20 roll."
To me, Fate of the Void (FotV) is talking specifically about the d20 roll and that IFotV talks about adding +1 to your FotV power. The only time FotV does anything is when it grants a +1. So the IFotV is saying that you get an additional +1 when FotV triggers. So, since FotV can trigger multiple times, so should IFotV.
I can easily see how others read it the other way and I could easily be wrong, I just believe you get +2 for each trigger. I believe that all those to hit bonuses ARE the benefit to playing a Starlock and through 8 levels, I haven't had better than a +6 and that has been rare. Can it happen more often and can it be more potent? Yes, but its not as often or as powerful as many people think.
At any rate, I can't believe that WotC has not put this on their Question of the Day (or whatever its called) and resolved this once and for all. For that matter, since they clarify some powers in errata I'm surprised the wording has not been updated there either.
Feel free to disagree, I just won't be convinced.
