I've spoken with my family without the 零 in numbers that are slightly higher (like 6070), and found that many people usually don't put the extra 零 in the number when saying it.
I have the same problem here - my logic tells me that you can't possibly get any other number than 6070 when you leave the 零 out. Can someone explain whether it would just sound weird, or whether it would actually cause confusion?
No. But you do start using that type of syntax when you get to the 100 thousands. For example, 万 (wàn) is 10,000 and 十万 is 100,000. Also, 亿 yì is 100 million and 十亿 is a billion.