Do you think driver “break in” is real?

No, I don't believe they do "break-in," What I do believe is people becoming accustomed to the speaker's sound. But lots of people also believe cables can be broken in, so there's that. 🙄

Hello sal1963!  sadly, "highest quality capavitors" is a bit vague. Unless they are Delunds, which are hideously expensive, that could be a problem. I have tried many different brands of capacitors (including Delund) and I have found that Mundorf KRPs work very well indeed and are reasonably priced. There are better sounding caps (Delund for sure) but the slight difference is not worth the price. I say this as a retired senior and serious, solder iron weilding, enthusiast. I'd tell you what brands they beat, but I am out of my house due to a flood and don't have acces to my amps, etc which are all in pods! The quality of the solder used, method of attachement of parts (super tight physical bonds before soldering) and the wire and terminals used in connecting the amps and speakers all matter too. I was shocked with the improvement made when I replaced connectors using ferrous metals with brass & copper parts! It made more difference that capacitors! When you consider that just in the wire from the amp to the crossover you might have four ferrous mental spades or banana plugs - then the terminals themselves on the amp and speaker boxes, the internal wire in the the speaker box - do the wires go from the crossover to the actual flexible wires to the driver's voice coils via a steel terminal attached to the speaker frame? - egads! (Fortunately my speakers are open baffle LX521s designed by Sigfried Linkwitz and it's easy to get to all the connections.) Make sure the wire from the crossovers actually touches the flexible wires going to the voice coils! Use silver solder. Solid silver wire used in jewelery making is available from jeweler supply houses at reasonable prices. it's not insulated, but you can figure that out. Details make a big difference! Enjoy the musc!

Absolutely.

We used to run across it all the time when I owned a stereo shop.  Brand new, sealed boxes from same shipment as our demo pair.   There was no doubt or question.

My Borresen X-3's are stated as improving in sound quality every 100 hrs. up to 500 hrs. I can tell you ....it's true.....

Driver break in needs about 5 minutes to get spider ready.

Then about 100-200 hours to get magnets and wiring and caps happy