BTC main value proposition is to be a decentralized currency and/or value store. 1. The BTC community desires it to be widely adopted by the population. But price volatility prevents so. A significant amount of people cannot afford the cost of volatility.
A big argument against inflation is that it raises the cost of business. The same argument can be used to criticize BTC. BTC volatility raises the cost of doing business if BTC is your only capital. If we desire BTC adoption to rise we must take care of BTC price fluctuation. BTC demand is highly unpredictable while supply is predictable, resulting in unpredictable prices. That means volatility can't change unless demand stabilizes.
To decide whether Bitcoin volatility will prevent adoption, maybe we should look at whether it has prevented adoption till now. The people who have been doing business with Bitcoin are pioneers with enough understanding to take on the risks you have mentioned above. Those who has bitcoin to spend have also been doing it to increase circulation and popularity.
A simple way to do it was by using BTC to spend and buying the equivalent in BTC on exchanges. For the merchants, They sell for BTC and convert part of it to Fiat to keep shop running. This is still an enthusiast's game and we haven't reached the stage where BTC should be your only way of doing business.
The primary purpose here is redistribution of BTC. It should be seen as very early stages of a long cycle of adoption. The next paradigm shift is going to come when Lightning Network and cross-channel swaps are fully deployed. Those will enable micro transactions and things like pay-per-view for content producers in the knowledge economy. Once this starts, its upto the participants to decide on how much of fiat they want to maintain as a hedge against bitcoin volatility. The path to adoption seems straight-forward enough but its a community project. Community being the catch word, nobody is going to come and propose that BTC is the best. Like say someone shilling a clone and claiming that its fast and cheap without explaining that it is so because of lack of scale.
What incentives do savers have to buy-in on a inflationary money supply? The incentive of stability? That's one reason people agree being exposed to the USD. Am I defending inflation tax? No. I'm asking could there be benefits to having a transparent voluntary contract with varying money supply rate. And I'm leaning towards a yes to this question.
The benefits to saving in BTC and not just in USD are many fold. A large part of the value that BTC has comes from its usage as a truly borderless currency. We still have to see how regulation plays out and these truly are the issues the community should be focussing on. The value also comes from underlying infrastructure and its usage. These initial days are filled with scams and clones but it should rationalize over time. If it doesn't, it will be the end for all these clones. Bitcoin movement on the other hand can still sustain itself for its supporters are much more clear about their motivations and aims.
Savings in USD or any other Fiat are subject to inflation as well as the "screw-up tax" that the public pays when central banks and banking behemoths screw up. BTC is much better in these regards.
If the supply of a coin could be influenced by price then we would have a more stable coin, the cost we pay is inflation. The issue then becomes an optimization issue, on what would be a proper trade-off.
Supply is determined by mining algorithm. Number of coins produced per blocks is part of the consensus rules and these cannot simply be changed by linking them with price. Its an idea alright, but i don't see any possible scenario on how this could be implemented without some sort of central control. We wrap back to the same question, do we need value stabilization when it is chiefly a centralized kind of decision?
The centralization associated with any stabilizing attempt is probably the reason nobody wants it.