if there were no further philosophical breakthroughs after, say, plato's death, would we be the worse for wear? is it the same ideas being recycled over and over, or are there real breakthroughs in collective human consciousness that occur overt time? nothing new under the sun ., . .
I understand what you mean. There are several factors to consider. Actually, two.
* The state of mankind (human reason)
Without revelation, human reason is limited in knowing many things. Now, the thoughts of philosophers we know are written down or communicated to us somehow. Every person's philosophical convictions are not. This is important. The philosophy of a society may need real breakthroughs, but I do not think on an individual level there is. Humans are not collective. We are individuals. This is why after each generation it is essentially a new beginning. Each generation defines itself. This is why the same mistakes are made constantly in history and why the only achievement of mankind to be transmitted in near its full manifestation is technology which is useful.
The Star Trek universe, where people have "collectively" overcome is nothing more than a choice of a generation. The next generation (he-he) could change that. Indeed, the Star Trek universe shows no new philosophy at all, and there is a lot of human dissension. It is merely a plot tool to explain the unity of mankind (so unified alien species can be introduced).
So, individually, nothing would be lost really, but for social influence, there would be. If the values of society pre-revelation were locked into a certain time period, there would be room for improvement lost. Remember, Plato was not the typical Greek at that time
That is why he is remembered.