In-Game Currency Converter

Because the bonus is added on top of the base currency amount, not applied as a discount to the item's price. A 50% bonus turns 1,000 coins into 1,500 coins for the same money, which lowers your real cost per item by the same ratio the currency increased -- roughly a third, not a half. To actually halve your cost per item you'd need a 100% bonus (double currency for the same price).

It's currency you already paid real money for but can't spend on your target item, because it's less than one item's full price. Wasted Money converts that leftover back into real dollars using your effective exchange rate, so you can see exactly how much of your purchase is sitting unusable until you either buy something cheaper or top up with another purchase.

Currency per Dollar (the effective rate) is computed from the TOTAL currency you receive, including any bonus, divided by what you paid -- so a bonus directly raises this rate. Real Money Spent is simply what you entered as the purchase price; it's an input, not a calculated result, so it only changes when you change the purchase amount itself.

Not quite -- they measure different things. Spending Efficiency measures how much of THIS purchase's money went toward something you could actually buy, versus currency left stranded below your item's price. A currency pack can have an excellent exchange rate (lots of coins per dollar) and still show low spending efficiency if the leftover after buying your target item is a large fraction of what you bought.