Imo it doesn't really make a lot of difference whether you do it now or later. You might get (slightly) more for your buck after he drops a star again and trains a bit faster but that's balanced by having slightly more to gather so takes (slightly) a bit longer.

And it doesn't make any difference whether he pops a star now or you keep the sp unallocated - he'll slow a bit to the 'next star rate' when he has enough whether you put them on or not.