Thanks for the replies.
I've been pondering this most of the weekend, and the thing that leaps out at me is the preponderance of caveats around Android. I guess having been in the Apple camp for so many years I expected more vociferous endorsements from the Android camp. The fact that so many responses here also remark on the stability and consistency of the Apple product is pleasing to see (for a generally bias-free response), but it also surprises me that Android isn't "better" in these areas. I guess I find it odd that a phone from a top-tier manufacturer like Samsung would have so many limitations. Battery drain for simple apps like Facebook or email seems bizarre, and does make me wonder whether buying into Android would be swapping one set of issues for another.
I also hit upon the key issue/dilemma for me. It starts with the smartwatch. My Garmin is leaving me wanting more, and the Gear S3 is calling out to me like a psiren. But the Gear S3 is only usable with an Android phone (specifically, a Samsung phone). So to indulge my smartwatch desires I would have to change handsets. And while the Note8 looks like a very nice piece of hardware, it sounds like I would be trading a stable and supported platform for a far more variable experience. So, to retain that stability, and to trade up in the smartwatch stakes, I would have to go with an Apple Watch. Which really doesn't do anything for me. I looked again this morning, and it really just doesn't excite me. I can't explain it any more. Maybe it would be different after using it in the real world for a while, but from the outside it doesn't grab me in any way. Plus, the Apple Watch doesn't inspire me with confidence that it would continue to be usable for more than a couple of years. I could probably make peace with a 4-5 year lifetime, but I think that would be stretching things, with even the first generation models already looking very long in the tooth just two years later. And then there's the price - $599 for the starting price, albeit same as the Gear S3, but it feels worse for a device that seems to be built to obsolescence. And then there's the iPhone itself. My iPhone 6 is approaching it's end-of-life period, currently 3 years and mostly okay. But if I did buy an Apple Watch then that means an eventual replacement iPhone. And when I look at my options there, I find it disappointing - a 12-month old iPhone 7 Plus would effectively be a size upgrade and little more (excluding Force Touch and the dual cameras) for $1419. The 8 Plus has the wireless charging, the dual cameras, faster processor etc, but if I want to avoid a storage downgrade would have to move up to 256GB and pay $1749! And don't get me started on the iPhone X! When I bought my iPhone 6 128GB three years ago, I cringed paying $1200 at the time, but I feel I've got good value over the years. The replacements are ever more expensive, but seem to offer little more than marginal improvements.
So my dilemma becomes even more convoluted: switching to Android really feels like a leap into the unknown, with a potentially variable and inconsistent experience, but the Note8 at $1599 seems like a positive bargain compared to my choices in the Apple system. The Apple products certainly are solid and well made, and give a reliable experience, but it pains me to pay those prices. And I still haven't solved my original dilemma about smartwatches.
I could just give the whole thing away, keep my iPhone 6 for another year, and hope that things improve with next years offerings. But I seriously doubt that the prices will improve (if anything they'll probably just get worse). There may be improvements to the issues with Android that have been raised here, but there's probably as much chance that they won't improve. I fully expect that if I wait another year, the model numbers will change but the key tradeoffs will remain. And my current phone will be a year older, and worth less for a trade in.
A few people have suggested practising with a "cheaper" phone, but spending $300-$500 to test the waters seems a little extravagant, and if I ultimately decide to stick with Android and buy a "forever" handset, then the overall cost is bumped up by the cost of the practice handset.
I really don't know what to do. I feel very conflicted by the problem (which is probably the most "first world" problem I've ever had - it's just a phone, for crying out loud!). I guess I'll just ponder it a little longer until I can make sense of it all.