I completely agree and had similar confusions. That's why I created this cryptocurrency spreadsheet so I could track assets in USD, BTC, and BTS. I needed all three to compare prices across various exchanges and coinmarketcap. When a price is good in one place for arbitrage (or just to know the price hasn't yet "caught up" so it's a cheap buy), I needed a way to quickly compare relative values in various currencies. You may find that spreadsheet useful. I've really been enjoying playing with it and improving my own copy with buttons which activate scripts and such (see the comments for more on that).

I've done the bitUSD loan thing a few times now and only this last one will I have to a wait a bit to pay down because BTS went down in value and I bought BTS with my bitUSD loan. I actually went 5:1 on that one just to be safe and not have to check it all the time. I also have a good amount of BTS on an exchange so I can increase my holdings a bit when things move around.