Question: Can lower stages of current rockets be replaced to reusable and more efficient boosters with parachutes? Would reusable rocket stages save money?

Answer: 
At [12 launches per year](https://spacenews.com/ariane-6-could-use-reusable-prometheus-engine-designer-says/), Arianespace does not see a business case for a reusable first stage.

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> “We still have not understood, would we save money by reusing? At least with our launch rate?” he asked. “We hope to launch 12 times a year. If we reuse 12 times, that means we only manufacture one time per year. It is difficult for us to have that.”
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> Bonguet said reusability would essentially erase the production efficiencies ArianeGroup is striving for, starving the Ariane 6 industrial base of the work upon which it relies.
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Now this is fairly specific to Arianespace's situation, where they have existing production facilities designed to build 12 stages a year, and no easy way to repurpose these for other work.

SpaceX solved that problem:

* they use 9 engines on the first stage (instead of just one)
* they designed the first and second stage to be as similar as possible, so the same facilities can be used, and a reduction in work on first stages is mostly compensated by work on second stages.
* they aim for much higher launch rates

Arianespace is hamstrung by lack of available capital to develop more radical changes, instead of the minimum-change Ariane 6 we have now.
Reusable first stages are already saving SpaceX money.

Parachute recovery has the drawback that your stage is going to splash down in corrosive salt water, requiring some cleaning and refurbishment before it's ready to fly again. 

Falcon 9 style powered-landing boosters have to reserve a lot of fuel mass for landing and optionally flyback.

ULA is proposing parachute & helicopter recovery for just the first-stage engines of their next-generation Vulcan launcher.