These are not new thoughts to me and this is why I started collecting low/midgrade Golden Age Action/Superman comics a few years ago. There appears to be great demand for these books and one doesn't have to be so grade conscious... a 5.0 is a very respectable grade for these books and my thinking is there will be long term demand for them, unlike midgrade Silver which is just too common.
Another area I've begun focusing on is high grade Bronze books -- specifically the series that I first read as a kid getting into comics. Stuff like 2001, Super Villain Team-Up, Machine Man, and Spider Woman. These books can be obtained in high grade for prices that us mere mortals can afford.
So, the next question is, 9.8 only or 9.4 and 9.6 as well? What is "high grade" in the Bronze Age? I'm going to try for 9.8s, but when nice 9.6 presents themselves for a fraction of the 9.8 price, I can live with a 9.6. Frankly, I believe that 9.6s and 9.8s are very close to being interchangeable and the difference is so minimal that I don't have a lot of confidence anyone could consistently differentiate between the two anyway.
So, let's start off with the latest acquisition: Super-Villain Team-Up #8...