Worth it? Depends on how much you value the gold. At this stage, where it costs 1250, it doesn't seem terrible. Four arena runs are what, 600g (150g each)? So for the remaining gold, you'd be spending about 7 packs worth of gold for better hero selections.
Presuming a uniform distribution of heroes, two picks has expected values of 33rd and 67th percentiles. With four picks, you'd expect heroes at roughly the 20th, 40th, 60th, 80th percentiles. The difference between the 80th and 67th percentiles is roughly the difference between Yogg/Edwin/Pyramad and Toki/Elise/Alex. Now, this *isn't* exactly a uniform distribution, but it's probably close enough to grant some insight.
Is it worth giving up 7 packs of the next expansion for 2 months of playing heroes a little bit better in BG? Well, that's up to you to figure out your own priorities.
For me, I haven't been loving constructed lately. I'll do my quests, most of the time. I don't care too much about the small number of packs. Getting the extra heroes is likely to show me, say, Akazamzarak or Malygos instead of just Sindragosa or Lich. It's not a huge difference, but there is one.
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Is it worth to buy it now? And when will the perks ends?