Calling all armchair generals! Boudica's Last Stand.

[Renatus]

One of the aspects of the 'return home' idea (my conception of it, at least) rests on the theory about the fall of Colchester happening in late autumn.

I still think that this is too late.  Tacitus tells us in the Agricola that the tribes took advantage of the absence of the governor to canvass their woes and to raise the rebellion.  It would make no sense to leave this almost to the time when he would be expected to have ended his campaign.  That is what happened in the event but that is probably because the conquest of Mona was achieved more quickly than might have been expected.  The comparative ease with which Suetonius seems to have overcome opposition on the island may be relevant when considering Agricola's apparent confidence in achieving the same result very late in the season and with only a limited number of troops (Agricola, 18).  From Boudica's point of view, there was no need to wait until the harvest.  They had the grain that was to sustain them until harvest-time.  They could start the revolt with that and seize whatever else they needed from Roman storehouses or pro-Roman tribes.

Besides, we don't really know how 'nationalist' her objectives might have been, whatever words Tacitus and Dio put into her mouth.

If by 'nationalist' we are thinking of the creation of a united kingdom of the British, that almost certainly was not in Boudica's mind.  If we assume that Tacitus had access to official records, including Suetonius' reports, and probably discussed the revolt with Agricola, we would be justified in believing that he reflected the contemporary Roman perception that her objective was to drive the Romans from the province.  This may have been inferred from the destruction of the centres of Roman influence and the general progress of the revolt or have derived from information gained from prisoners or perhaps from tribes that had been canvassed to join the revolt but had not done so.  Nevertheless, it is a perception that may be taken to have been held by those close to the action and is very likely to have been accurate.