As with all straddles/strangles, the biggest downside of buying when IV is high is the risk of IV collapse. Of course if you get a big move, the gamma gains will more than offset the vega and theta losses. But if the move is not big enough, and your position is close to expiration, you have negative theta and negative vega working against you. So I would consider it as high risk high reward trade.
As for trade management - personally I prefer to close both legs. If you close only the winning side (calls in this case), you are taking directional risk and betting on reversal. The only exception is when there is very little value left in the losing side, so it might not even be worth it to close it.