Specifically, however, I am indicating by my post that I'm not willing to pay 4x the price, for privilege of sharing - it does not have that value to me and it's not where my expectations were level-set :). [I currently use ToDoist which makes it easier to start (no privileges/contact sharing required) and add guest-editors/share]
My post is meant to provide feedback: I'm currently not trying their product (and I've explicitly provided why - the seemingly minor request to share my contacts), and I may not become paying customer once I figure out a way to try it (because the jump to my desired level of service is too high). It is up to the developers, if they read it, to gauge how representative I am of the target audience and therefore how relevant my concerns are; I'm assuming somebody like Pateo11 would quickly setup A/B switch - signup with and without asking for contact permissions, and see the impact :)
I would hardly say "no appreciable improvement". IMHO it's appropriate to price products based on the value derived, not the effort to implement each incremental "feature". And the ability to share is the most human feature. We are social creatures. To share and collaborate and be relational is to be human :)
So the price jump feels fair to me. We can get near full-knowledge of the product at a reduced price point, but to be human with the tool, we get hit with the real cost :)
EDIT: I also don't like the actual pricing structure, but that's only because I would rather participate in co-operative systems, and dislike capitalist ones. The above comment is my putting myself in their shoes :)