My opinion would be go with a conventional system versus ductless.

Having said that I'm using ductless cassettes in a project that I'm involved with mainly for the individual room temperature control they give,reduction in duct work, and some hoped for energy efficiency. Also the system I'm having installed can simultaneously provide heating or cooling from the same condensing unit...one room calling for heat another for cooling at the same time.

I have found the same thing you have regarding initial costs begin higher with ductless mini splits.

In my home I have a large added on sunroom that did not have space for duct work so I used a mini split and it does a very nice job. I just think you need to use them in the proper applications.

What is your climate like? It makes a difference. What fuel is available to you, electricity only or natural gas too? Right now, it is a lot less costly to run a gas furnace than a heat pump in most areas. If, like me, you don't need much heat that is not a big deal.

Conventional split units can approach the efficiency of MSHP, but then you have the duct losses if the ducts are outside of the house. Keep the ducts inside if you can.

Retrofits are a strong suit of mini split systems. Fitting ducts into an existing structure is difficult. Losing that space is costly too and that is what is obviously bothering you. Double the dollar cost seems too high to me too. Get more estimates. Keep in mind that there are MSHP heat exchangers that can do more than one room and have short ducts. They can help make for a nice design in the right home along with high wall units and ceiling cassettes.

I currently have central air with gas heat. I lived in the Middle East for years and our flat had mini splits in every room. I far prefer the mini splits. We had The LG art cool units and they worked incredibly well. Our living room was about 700 Sq ft with 12 ft ceilings and two long walls with floor to ceiling windows and temperatures that stayed over 110 degrees. Our units would freeze us out of the room if we were not careful. The real power of mini splits is the variability each room can have a different temperature. Having said that as great as they are at cooling where I live now has far too many heat demands to give up gas heat.

Having said all of this I can't help but think that mini splits are a 50 dollar solution to 2 dollar problem. Those spaces are huge for just duct runs. You can probably reclaim 90% of the closets just reworking the ducts. Not to mention wall stacks if you really need the space.

bry911, at most, mini splits might be a 3 dollar solution to a 2 dollar problem. At best, 1:1.

I assume that you were in a very arid climate in the middle East. One important feature of variable-speed cooling equipment is their superior ability to remove humidity in low-load (sensible heat) conditions. You did not get to experience that! Large, variable-speed ducted systems might be able perform as well as mini splits on paper, but then you have continuous air flow through, often leaky, relatively poorly-insulated ducts. They might be continuously-condensing ducts at that point if they are outside of the house envelope.

In addition to that, the capacity of a large central split system can not be throttled back to the low output a smaller mini split. That all yields potentially better humidity removal.

Bry911 makes good points about reworking the duct placement. The typical placement of ducts in retrofits is outside of the house. I have seen wonderful retrofits where chases are incorporated into the interior design and look like they really belong to the room rather than being add-ons.

The link below is a nice summary of why putting the ducts inside is important and has some pictures of good approaches. I am sure that lots more information can be found on that web site and others. Some HVAC people might be good at retrofitting with boxed-out, furr-up and furr-down areas and making them look good, but that is really not their job. If people are not good at it themselves, it might take a designer to get it done well.

Here is a link that might be useful: Building science

I am afraid you are somewhat mistaken about Middle East climates. Most of the populations in the Middle East exist near water. I lived on a small island in the ocean that saw little rain but the sun beating down on the water made every single day extremely humid. But not to worry since the temperature would drop 35 degrees every night and the supersaturated air was so moist that a trip to the mailbox leaves you soaking wet.

I stand by my 50 dollar solution to 2 dollar problem. The problem as stated was "ducts are taking up too much closet space," and he was kind enough to provide a picture. There may be goods and bads about both systems but in the end (assuming the provided diagram was correct to scale) then reworking duct runs in an area which will already require construction will be a hell of a lot cheaper than buying a bunch of mini splits if your goal is to reclaim closet space.

Thanks for all of the helpful tips. We have come along way since this post. As you can see in the updated plans, the whole room is much more open and free of all the HVAC obstructions. We only have a small HVAC duct/column in the center of the room which also doubles for a support beam. The key was moving the laundry room off to the far wall against the bath #2 wall and moving that bath #2 door off to the left so that we can fit the W/D side-by-side. We are finally getting excited about these plans. It has been a long journey.