While I understand Dracosuave's argument (and think that it is technically correct), to me it doesn't capture what I think is the intent of the power.
First of all, if the sustain doesn't allow the pull, it basically does nothing at all. Rather, all it does is create an action tax on keeping the target dazed - meaning that the target becomes "undazed" either when it makes its save or when the Wisp fails to suspend an action to sustain. IMHO it adds nothing to the power and is rather inelligant.
More importantly, it doesn't capture the spirit of the Wisp. Basically, the Wisp's whole "schtick" (both in D&D and the myths/stories from which the D&D monster is derived) is to ensorcel (aka daze) travellers (aka the target) and then cause them to walk off into the swamp (aka the pull) where they perish due to environmental hazards (quicksand, drawning, etc.). If the sustain doesn't allow the Wisp to repeat the pull, the power really doesn't capture the "feel" that I feel the creature and this power ought to have.
That said, I do realise the power is very poorly worded for how I think it ought to work. Rather, IMHO the creature is best served by changing the sustain language to specifically indicate it allows the Wisp to pull the target again, or remove the langauage and give the Wisp another power which reads:
Minor action
Target: any creature currently dazed by the Wisp's Luring Glow
Effect: pull target 3 squares
I do realise either change would be a houserule, but it does allow the Wisp to function how IMHO the designers intended it to.