That is the big question, Band on the Run. And I don't think there is a clear answer. On the one hand, the gospels do reflect the situation and time from when they were written, and it is clear that conflict between Pharisees and early adherents of Christian Judaism (with early Christianity construed as a Jewish messianic movement) was particularly intense after AD 70 — much more so than in the earlier period. Some view the passage (and other statements in Matthew) as reflective of a deepening rift between the Matthean community and the Pharisees on one hand and the Pauline community on the other (who may have been targets of some of the criticism in ch. 5-7). That is what I recall is the viewpoint in David Sim's Apocalyptic Eschatology in the Gospel of Matthew. The arguments for this viewpoint also depend on what synoptic theory one holds. If one regards the parallel in Luke 11 as reflecting an underlying common source (Q) utilized by both Matthew and Luke, then one could cite that as evidence that much of the material in Matthew 23 is considerably early (and more likely to have been spoken by Jesus) which then was later redacted by the author of Matthew to reflect more current concerns. Or if one holds to the Farrer-Goodacre theory (which rejects Q as a source of both gospels), then there is less reason to consider that the material in ch. 23 (added to Mark, written in the 60s) is older than the gospel of Matthew. On the other hand, one could certainly also argue that the author of Matthew used an earlier source (M + Q material, added to Mark) for this material, with the sayings representing early Jesuine tradition. If Jesus was an apocalyptic prophet like John the Baptist, then it would not be unusual that he would criticize the religious leaders of the day in language as harsh as that attributed to the exilic prophets of the OT (such as Jeremiah and Ezekiel). Apocalyptic literature of the period was filled with harsh condemnations of religious leaders; the polemic against the "Seekers of Smooth Things" in the Dead Sea Scrolls and the apostate priests in the Testament of Levi come to mind. I think it is pretty clear that much of the content in the "woes" reflect older pre-Christian religious polemic. One can find parallels between the following and ch. 23 of Matthew:
Damascus Document (CD 5:11-17, 6:11-19, 8:3-13): "They defile their holy spirit, for with blasphemous tongue they have opened their mouth against the statutes of God's covenant, saying 'They are unfounded.' They speak abomination against them. They are all igniters of fire, kindlers of blazes; webs of a spider are their webs, and their eggs are vipers' eggs. Whoever comes close to them will not be unpunished; they guiltier he shall be unless he has been compelled. For already in ancient times God visited their deeds, and his wrath flared up against their actions, for there is no intelligence in them....But all those who have been brought into the covenant shall not enter the temple to kindle his altar in vain. They will be the ones who close the door....They should take care to act in accordance with the exact interpretation of the Law for the age of wickedness: to keep apart from the sons of the Pit, to abstain from wicked wealth which defiles, either by promise or by vow, and from the wealth of the Temple and from stealing from the poor of the people, making widows their spoils and murdering orphans, to separate unclean from clean and differeniate between the holy and the common, to keep the sabbath day according to its exact interpretation, and the festivals and the day of fasting....The princes of Judah are those upon whom the rage will be vented, for they hope to be healed but the defect sticks to them; all are rebels because they have not left of path of traitors and have defiled themselves in paths of licentiousness, and with wicked wealth, avenging themselves, and each one bearing resentment against his brother, and each one hating his fellow. Each one became obscured by blood relatives and approached for debauchery and bragged about wealth and gain....Their wine is serpents' venom and cruel poison of asps. The serpents are the kings of the people and their wine is their paths....But the builders of the wall have not understood all these things, nor those who daub with whitewash, for one who weighs wind and preaches lies has preached to them, so that God's wrath has been kindled against his entire congregation".
To answer your other question, anti-Pharisee sayings are found in ch. 11 of Luke in a somewhat different form, and there is a short parallel in Mark 12:38-40 with respect to the scribes. There are also parallels in the Gospel of Thomas (particularly, logion 39 and 102), as well as the Gospel of the Savior:
Gospel of Thomas 39, 102: "The Pharisees and the scribes have taken the keys of knowledge and hidden them. They have not entered, nor have they allowed to enter those who wish to. You however be as wise as serpents and as innocent as doves....Woe to the Pharisees, for they are like a dog sleeping in the manger of oxen, for neither does he eat nor does he let the oxen eat".
Gospel of the Savior (POxy 840), lines 31-45: "Woe to you blind men who do not see! You have bathed in only these natural waters in which dogs and pigs lay night and day. And having washed, you have wiped the outer skin, which also prostitutes and pipe-girls anoint and wash and wipe and beautify for the lust of men, but the inside of them is full of scorpions and all wickedness".
