My solution is get girls to 98% 2nd affection then wait for scenes to come. 2% is not a lot of wasted stats after all so it's no real loss not having it for a while while that 98% extra is VERY nice.

personally went for the affection, prehaps some one can crunch the Maths, but 3%"slice attribute" for three knights....seems well not much compared to 4 knights with 90% 2nd affection, and that with change left over. as some one pointed out the necklaces seem to be permanent sale items, BUT who know maybe Nutaku will remove the necklaces later, but currently the necklaces period is "unlimited" so i guess they are here to stay.