I think we should always be careful when speaking about the old cultures. We have been very polluted by all the films made in the 20th century and in this, surely the Roman culture suffers a lot more than the Greek, which has always been overshadowed by the other. Just as an example, ask someone the names of the Gods of Love, War and the King of Gods in classic pantheons: chances are they will say Roman names. And by the way, we even have a TV-series where 'Hercules' goes along with Zeus, Aries and all other Greek names..... safe that Hercules is the roman version of Heracles. Got it?
That said, I'd also be very careful regarding admiration for Roman culture. That is an empire that has been many times admired and immitated, and two striking examples are the Napoleonic France and the United States. There are too many things in the US today that seem inspired in the Roman Empire: the Eagle, the Senate, the Capitol, the admiration for strength and violence as worthy aspects and justified means to solve problems and even the notion of a 'pax americana' to be imposed somewhere, that sometimes crops up and is nothing but an allusion to the 'pax romana'.
As such, I say that the Roman bad traits may have been very laundered in the states.
From what I've read, it's hard to find a period in Rome, even before the empire, when there were no strikes against the ruler, and no attempts to kill them, and when I try to think of a period when I'd like to have lived there, and Roman history lasts for more than 1000 years, I'm at a loss to find one. Really, no one seemed particularly good. Whereas I could easily have lived in Pericles' time.
Of course, that is just an opinion.
As for the wars between Athens and Sparta, the Peloponese wars, they were different warring city-states, therefore, different independent entities. But they shared a notion of culture: language, myths and habits, so much so that when Persia invaded, they still found some kinship against the invader as Greeks. In a way, they are similar to the Celts, who were also divided in different independent clans with similar cultures but who, on the other hand, never got to unite against a common foe and, for that reason, were defeated.
The Greeks, at least, defeated the Persians. It's true that some key concepts developed in Athens, but it expanded outwards, and there are many philosophers and mathematicians from that time that do not come from Athens. Actually, the greatest ones are always associated to other cities: Thales of Mileto, Pitagoras of Samos, Archimedes from Syracuse, Eudoxus from Cnido, and so forth, and so forth. And remember they had a notion of being only one, for they coined the term Pan-Helenic to acknowledge all peoples of Greek culture.
Finally, please, Athens and Sparta are NOT colonies of anyone. They are the founders. THEY created colonies, along with other Greek cities, in Asia Minor and Italy. Those other cities are the ones that must be called colonies, not the original settlers.
Oh, and for Greek culture, I do think the best book to read is Paideia by Werner Jaeger. I once read about 100 pages from it.... a staggering 7% of the total.
Alex