Sound quality of Newer versus Older speakers

The speakers in my main system are 40 years old. I paid $264 for them about 4-5 years ago. They do some things remarkably well. I'm sure they can be bettered but I enjoy them tremendously. I just don't see any reason to spend 10X more for a little improvement when I'm already enjoying myself so much.

One area where I think we are in much better shape is in tweeter technology.

For a traditional speaker (not horn or ESL,etc.) tweeters have achieved remarkable extension and low energy storage. The innovation of the ring radiator moved the bar up considerably for what could be done with an inexpensive tweeter.  Top level AMT show remarkably low distortion or thermal compression in addition to extension.  It's easy to find tweeters that are flat through 20 kHz even among soft domes.

While the idea of Be tweeter diaphragms has captured the imagination, they vary greatly in quality and are now equaled or bettered by others.

Another might be how inexpensive really good film caps are now.

It is a very big question.
Vintage speakers are very different, from electrostatics to horn.
There are also different time periods.
For example speakers from 50x-60x are different from speakers form 70x.
What I don’t like in the speakers evolution, it went to direction of small and low sensitive designs. That makes sound more compressed, tiresome and unmusical.
The second think I don’t like, many modern speakers designer try to emphases high frequencies and it makes speakers sound unnatural.
I also don’t like the fact the new speakers are designed to play modern POP music that makes them sound worse for classical, vocal and jazz music.
I also want to add the "new" materials like beryllium are not really new and have been used in speakers industry since 80x.
Here is an opinion of Peter Qvortrup about it:
https://parttimeaudiophile.com/2018/01/25/peter-qvortrup-high-fidelity-the-decline-of-the-decades/
For people why think that vintage speakers are garbage can listen this video of Jensen D4 field coil speaker 9" from 1920's. 
https://www.youtube.com/watch?v=nTRcg7DCuMQ

Regards,
Alex.

From a sound quality perspective, is there anything that newer speakers are doing better than older speakers.

Uh, yeah. Everything.

There was no need for subwoofers with the older speakers, unless they were bookshelf type.  Even some of them did a reasonable job. 
There was a push for "clarity" in the late 70's and onward for mids and highs to be extended. Now, even with floor standers you need a sub to cover the low end frequency. I understand the need to cut back on the low frequency to get clarity but the pendulum has swing too far imo.  But it has created a new market for subs that didn't exist before the great push for midrange.