Good points both; and agreed that Tacitus looked back to a "Golden Age". It would be nice if we had a dozen contemporary histories of Britain during Agricola's time, so we could slice, dice and compare. But, one has to start somewhere.

I confess more familiarity with his "Germannia" than with his "Agricola". As to the former, one can find many points of controversy and also unknowns (e.g., what population group or geographic location was he really talking about). Moreover, he had to rely on secondary (and more remote) sources for much of his information. So, there is an inherent unreliability there.

"Agricola" seems more of a "family history" type work - and, as such, one expects the better side to be emphasized - with some family legends thrown in. Like most classical historians, Tacitus composed the speeches of his characters - how closely to the original substance, we do not really know. The speech of Agricola to his troops (Agricola, sec. 33-34) may have come from Agricola's recollection of that day.

The speech of Galgacus is something else. We may be assured that no Roman was there to record it. One wonders if that speech is not Tacitus himself. If so, it has value as an expression of a view which would have run against the prevailing "wisdom" of his time; a safer way of expressing dissent in those times.

In Tacitus' view, "literary critics" played for keeps in that era. So, as to panegyrics, we have:

"2. We have only to read that the panegyrics pronounced by Arulenus Rusticus on Paetus Thrasea, and by Herennius Senecio on Priscus Helvidius, were made capital crimes, that not only their persons but their very books were objects of rage, and that the triumvirs were commissioned to burn in the forum those works of splendid genius." (Agricola, sec. 2)


Refs.

Tacitus, Germania (partial text)
http://www.fordham.edu/halsall/source/tacitus1.html

Note: Here is an example of some truth and some mush:

"Upon the Suiones, border the people Sitones; and, agreeing with them in all other things, differ from them in one, that here the sovereignty is exercised by a woman. So notoriously do they degenerate not only from a state of liberty, but even below a state of bondage."

The Suiones are generally thought to be the Swea (Swedes). There is an area in Finland, across the Gulf of Bothnia from Sweden, named Sideby in Ostrobothnia. So, some have inferred that the Sitones lived there.

The Kalevala Saga (Elias Lönnrot), in part, recounts the wars between the "SE Finns" and the "NW Finns".

http://www.sacred-texts.com/neu/kveng/kvrune47.htm

Among the latter, we find that the main character is "Louhi, hostess of Pohyola, Northland's old and toothless wizard, Makes the Sun and Moon her captives ..." The Finnish for Ostrobothnia is Pohjanmaa ("Northland").

So, if Sitones = Sideby (definitely in Pohjanmaa), the Kalevala gives some support to Tacitus' factual claim (1st sentence above). Since the Ostrobothnians make the claim (usually to government types): "We are free men, not slaves.", they would have problems with Tacitus' conclusion (2nd sentence).