Ask HN: Is there such thing as being too nice in customer support?

I run a specialized ecommerce platform, and I feel like I'm doing consulting work instead of offering a $X/mo SaaS product. Customers would email me tons of feature requests all the time, and, I, being nice and accommodating, would try to implement everything (within reason) in hopes of retaining them. I may have retained them, but it doesn't stop the barrage of feature requests that come in all the time. In fact, they have started to think that it's their right to demand features with deadlines etc. by paying an extremely small retainer (the SaaS fees), so they take it for granted.

How can I just say no? Especially when I know whatever changes they want are usually just beside the point, in that they are not addressing the bottlenecks of their businesses? I have tried "We will take your request into consideration." but it never turns out well. They will come back a few days later and go, "So how's the progress with irrelevant/peculiar feature X? I think it will be a good addition to your platform!"

The worst cases are when customers think that they're doing me a favor with their clever suggestions, saying things like "Aren't you glad that I'm giving all these good suggestions for free? Maybe I should come to work for your company." And they have no idea about the impact these features have on their conversion and sales; they don't even know what A/B testing is and prefer to use their "instinct" and "design acumen" in determining whether a feature is good for their business.

What would you do in my position?