Have speakers really improved within the last 20 years??

Ah, the age old question, Ginger or Maryann? Like hearing, this changes with age :)

In spite of the fact that this seems to be a recurring trolling thread, I’ll offer my experience. I have 2 systems. One has brand new Goldenear Triton One.r speakers. The other has a 20 year old Audio Physic Scorpio - about equivalent in price. They are comparable in sound quality. The AP has better imaging. The GE has better bass and slam. If I didn’t know, I wouldn’t be able to tell which is newer.
I’m sure that speaker design has improved over the last 20 years, but some older stuff is really good!

There is no one single measure that I know of and I both like and hate the, 'how does it sound to you' answers.  The huge difference over the last 20 years is found in 'material science'.  The raw materials have developed in all aspects of audio into new 'materials' and this is true from the material for cones of drivers to the construction of electronic components and the qualtiy of everything from contemporary Cardas copper wire to silver lined capacitors, etc.  The new materials allow for higher SPL/sensitivity without loss, and in fact performs much better than weak/low spl speakers.  If you take apart a common 1970s speaker you will find lots of really crappy junk stuffed into them:  Sony, Bose, Sansui, Henry Kloss's ARs and Advents, and even Magnavox et al.  
If you start with speakers from the 60s and 70s you are able to track the change in design and materials better and able to see the trends that began in the 60s and are still 'trending' today.  And it also depends on which speakers you are talking about.  Kenjit describes a cheap commercial speaker and is accurate.  If he took a close look at a pair of $140,000 Focal speakers it does not look at all like his description.  There is alot of room inbetween!!! 

My understanding is that desktop engineering programs have improved significantly. Engineers can work through design iterations much faster. Reflections, resonances, stress, etc can be analyzed quickly and accurately. This has led to better designs across the board. 

Use your ears. If you don't hear a difference between speakers manufactured decades ago and some of what's available now, count your blessings. You'll save money.