Great discussion! A few things in play here. Pricing will always be dynamic as long as consumers want more than just low prices, and since not every consumer puts price front-and-center all the time, retailers will have the freedom to exploit that with smart pricing algorithms that fine-tune themselves. More data over time makes them smarter, and I suspect those same algorithms will one day soon be offering the price-first consumer a sharper price than the service-first consumer gets on the same item. Whatever retailer understands me the best will earn my loyalty.
I've saved lots of $$$ over the years with camelcamelcamel.com by uncovering what constitutes a great price on Amazon, then I save the item in my shopping cart until I see the price drop (which I get alerted to anyway if it's saved in my cart). With very few exceptions, I'm still buying the item on Amazon. I agree with the earlier comment re: perceptions about jittery prices causing some consumers to pull back from automatic re-ordering. That's a clear watch-out, but dynamic pricing is part of the future of our industry, for sure.