Julius Caesar exempted Judea from tribute in sabbatical years but it's unclear whether or not Herod the Great continued under this policy. After Herod's death, his son Archelaus seemed to ignore the sabbatical altogether and we can only imagine what revenue he might have collected from any Jewish landowners who remained observant in 2 BC and AD 6.
When Rome took direct control they introduced a poll tax (tributum capitis) but did they continue the land tax (tributum soli)? Mary Smallwood presumes they did and also presumes Caesar's exemption was abolished at this point, but for all we know it was abolished earlier. Peter Richardson cites Josephus as strong evidence that Herod the Great was less than completely respectful of the tradition in 30 and 23 BC. So I ask, since the King evidently collected some tax in those years, wouldn't he also have shared with the Emperor?
We can only guess what the King did in 16 and 9 BC, but even if Caesar's policy was still good after Herod's death, the subjects of Archelaus didn't need the extra ammunition to get him removed. Since this is still a push, I question only the double presumption by Smallwood. If the land tax continued after 6 AD, how could the exemption be removed only then without any mention of complaint or compensation? The zealous rhetoric of Judas was far more anti-Rome than anti-tax. The 'galilean' also didn't need the extra ammunition.
To speculate for just a moment, it is possible the poll tax could have been a clever compromise if the land tax and exemption were abolished together. Quirinius' property assessment would then merely have told him the proper amount to assess 'per capita'. If it could be proven in fact, this would give the debate referenced in Mark 12 an additional depth - with one side arguing the poll tax was acceptable because non-agriculturally based, and the other side viewing all seven years of poll tax unlawfull as a deliberate runaround on the whole sabbatical tradition.
This conjecture would fit perfectly if we had some reason to think Judea bucked precedent and gained exemption from the land tax altogether. It could fit the pattern of privleges issued by Rome, but without specific evidence it remains merely one of two presumptions. However, if we take the other one, Smallwood's, we should probably conclude sabbatical related outrage died down slowly through the reigns of Herod and Archelaus. And thus in turn, Smallwood's second presumption, that Caesar's exemption was still in place up to 6 AD, seems likely to be true only in an official sense. Practically speaking, it must have been virtually forgotten, made moot by decades of neglect.
Personally, the more I think about the poll tax as a compromise, the more I wonder why the trap question in Mark 12 is supposed to matter without sabbatical implications. (Even if they were merely fishing for zealot sentiments, were the Pharisees really so concerned about the image on the coin? Isn't that what they had the money changers for?) However, I don't normally find creative inference very convincing without additional support and I could be missing something here. Therefore, I'll be just as happy (for now) to stand with the conventional view that Judea probably continued to pay land taxes after 6 AD, including sabbatical years.
In conclusion, I have to say neither view affects our assessment of daily life anyway, as far as I can tell. Only wealthy landowners were directly affected by the land tax, however long it lasted, and the question may depend on how many of those were also devout enough to remain strictly observant. Since we're going to presume that those who let their land lie fallow were still going to be taxed on it, it seems simple enough to further presume they simply stored up extra money during the first six years to use for a tax payment while they lived off their stored grain and produce. This should only seem unnatural to anyone who ever said religious devotion comes at no cost. (!)