Difference between today and yesterday.

I would say - oh no - Paper vs Plastic. Most old speakers were exclusively paper cones, while most, but not all modern speakers use polymers.

Some say that speakers peaked in the late 60's to mid 70's and then went down hill after that.......

It depends on the music. For "big" music, symphonies, organ, loud rock, etc. the old JBL, Altec, and the like with 15" woofers are best. But you can't play such speakers at realistic volume in an apartment, and the speakers probably wouldn't fit anyway. For pinpoint imaging of a female vocalist with piano accompaniment, (which seems to be the official audiophile test signal these days) modern speakers excel.

I couldn't live in an apartment, or even in a development with houses close together.

A lot has been gained in the last 20 years in the area of materials used in the manufacture of speaker systems. From the use of gold/rhodium plated, oxygen free copper 5 way binding posts(for a better connection), higher quality (tin foil/teflon film, polypropylene, polystyrene) capacitors for improved signal transfer, stronger magnets( barium/strontium ferrite, neomidium) for higher flux density, stronger and lighter cone and dome materials(carbon fiber, titanium, diamond) for less flexure/distortion, faster response. Denser, stiffer cabinetry to reduce resonance/coloration. There are a vast array of modern speakers that can play at very high SPLs, and yet sound like real music, unlike the Junk But Loud of old. Yes- the professional speaker manufacturers built some systems for home use, but the quality of the drivers/x-overs in those systems never approached that of their sound reinforcement equipment. The horns that were designed for projecting sound far into an audience, when used in a home environment, could generate a headache faster than a jackhammer with their peaky responses, and metalic resonances. Much has been gained/learned with regard to horn systems as well, and the old can't even compare with current designs acoustically(Acapella/Avantgarde). Of course the way we test/design systems has changed drastically as well. The proof is always in the sound though, and naturally: There are those that can't hear the difference, and will claim there isn't any.