Having followed Apple for a long time, I'm always impressed at how 'oh my god the next one is going to be sooo much better' there is floating around. Ignore it. What if S8 comes out and it's...the same as S7, but with one extra sensor you don't care about?
Don't make a decision about a hyped product that doesn't exist. Analyze S4 vs. S7. Me, personally, I went from S0 to S4 and loved it; I'm planning to upgrade to S7. I'll get the $100 trade in and do aluminum, so it'd be ~$300 to upgrade for a bigger screen, newer internals, and all around better product. If S8 is truly that mind-blowingly awesome, I'll just eat the $ on that upgrade. But the rumor mill is always saying how the next one is the one to get. Literally the day before the 13 announcement, they were hyping the features on the 14 (OMG! fingerprint scanner! no notch! cures cancer!).
Love the tech you have, don't pine for a hyped product that doesn't exist and won't even be announced for a year.
A very real scenario for me, though, was that the wife OK'd an upgrade of my iphone X in July. At that point, it was worth waiting a couple months for whatever I knew would be out in September. But even though 13 vs. 12 ended up being a minor upgrade, I knew it was going to be updated, so I was willing to wait a couple months. But not buying b/c the rumor mill's fantasy land specs didn't come out?