Loudspeakers have we really made that much progress since the 1930s?

Agreed. Transducer design has not changed for decades. Mostly tweaks. Some older designs are extremely good even against the best available today. 

From my perspective, the biggest step change was when transistor based power amplifiers allowed greater flexibility in speaker transducer design and realistic LF bass frequencies. Greater power in power amplifiers has allowed wider directivity and less efficient transducers to be employed and active designs allow for better integration. 

So the 70's was when a step change occurred. Arena rock and the golden era of the recording studio helped drive the technology.

I think microphones are the aspect of audio that has not progressed much and even if so most  engineers are using vintage mics or newly built ones with using old topologies.   
I have a very novel concept for mics and tried to pitch it to someone once, but it would be expensive to develop since it uses no diaphragm 

So..it appears that John is right, there is no innovation in a true meaning of it, just some improvements in certain areas, maybe.
Speaking of cars, not from 30s. The original BMW M3, small and light, was a true driver's car. The same with Porsche. Now look at those modern computers on wheels that those cars have become. I don't need them.

I used to run a Ford Bronco, because I could load my hang glider on it and get to the top of any mountain that had a road up it. It had no computers and was easy to service, being very simple.

I replaced it with an Expedition, which has about the same cargo area. Despite having an automatic (the Bronco had a 5-speed overdrive transmission), the Expedition accelerates faster, due to having about twice the power, handles better, is very quiet inside, is also much more comfortable and despite the computer is a lot more reliable and just does not need the service all the time like the Bronco did. On top of all that, it gets about 3 mpg better mileage. That is a difference that was wrought in the space of about 25 years.

The funny thing is, the basic designs of the two are really similar.

This is true of speakers too. But if one ignores the effect that materials science has had on speakers one might likely throw out the baby with the bath. Kapton didn't exist 70 years ago. Neither did highly regulated power supplies. The impact of the Theile/Small parameters can't be ignored.

If I were to point to one thing that has really affect high end audio in the last 30 years its how we manage vibration. Speaker cabinets are much more dead now; literally that's the big improvement in most turntables, and killing breakup in drivers is still a pretty big deal.

I like the older designs but there's not a one of them that won't break up.

Its up to the individual to ascertain how important these improvements are. For my own part, I appreciate the size and efficiency as well as the refinement offered by the new technology that simply isn't there in older designs. 

But I make my own recordings. I know what they sound like...

But I make my own recordings. I know what they sound like...

I presume that applies to all recording engineers......?