i quite agree that we do not know where Eve got the "do not touch" instructions from. i also agree that it simply will not do to "shift blame" from one to the other. It affects the argument not one iota, but still leaves us with the thorny problem of imperfect worship.
Now we will take a look at your "strong" argument, based on Inspiration
...here's my stronger counter-argument, attending to the Infallibility of Scripture: God did not say, "neither shall ye touch it lest ye die". How do I know this? Because neither Adam not Eve experienced Spiritual Death when they touched the Fruit of Trial -- but only when they ate it.
Here are my counter arguments to these propositions:
1) We cannot know if Adam and Eve suffered Spiritual Death or not, because the acts of touching and eating are not sufficiently separated in time for us to make that determination.
2) We have no record of what would have happened if they had touched but not eaten.
3) This is incidental, but merits consideration: scripture records that their eyes did not open until both of them ate the fruit. Would this not imply a "delay" function, rendering the "touching only" point moot?
The result is that on this point, we are still dealing with unknowns. Now it is true that i do not read Hebrew, and am not qualified to look at the language structure to make determinations. i have looked at the LXX, which i can read, but it still gives me the same problem, namely that it is a translation (one from Hebrew to English, the other from Hebrew to Greek). For what it is worth, no additional information is to be gleened from the LXX, the verbs being simple aorist indicatives, and aorist participles.
This next section will be the most difficult for me to counter, but the attempt will be made for the sake of completness.
In the first place, if we only had the Gospel of Mark then it is true that we could not prove that Jesus said "Tetelestai". But we don't just have the Gospel of Mark; we have everything that God intended us to have, included the Gospel of John. So I don't think that we can apply a "Were we to look exclusively at the Gospel of Mark" paradigm here because there's no "4 books of Genesis"; we have in Genesis everything on these subjects that God intended us to have. When we consider the Gospel of Mark exclusively, we nonetheless know that there is additional Infallible information about the Life of Christ in the other 3 Gospels. Genesis, OTOH, is complete in itself insofar as God intended to Reveal; I think that, given Sufficiency, it's a difficult argument to suggest that maybe God did also say "neither shall ye touch it lest ye die" and just didn't see fit to tell us so in Genesis 2:17 which records His Commandment. However...
You would be correct in saying that the "If we were to look at the book of Mark" paradigm does not apply to us, however it did apply to the first believers. You may recall that until the New Testament was completed, God's revelation to His people was progressive. After the New Testament was compiled that revelation was complete. The issue here is the Providence of God, providing sufficient revelation for the purpose of bringing His elect into the Kingdom. The believers in Rome (where Mark wrote his gospel), for example, could not know that Jesus uttered the word tetelestai, while believers in Ephesus (where John resided) would have. The fact is that God's Providence has brought the totality of his universal specific revelation together as his elect were further removed in time from the events. The argument is that we have that knowlege, all of them did not. There are things that we still do not know...just what did the seven thunders utter...
Having said all of this, i confess to you that i really am not capable of determining just what Genesis 3:6-7 says, because i lack the language tools, and must rely on translation. i tell you that i am also confident that the Orthodox Presbyterian Church, in accordance with the tradition of biblical scholarship began by it's Spiritual human founder, J. Gresham Machen, will sort these matters out to the satisfaction of those who will not hide from the truth. i look forward to the results of their inquiry.
Oh... do they grow on TREES?
Well, the first argument isn't watertight IMHO. I threw it out there because I thought it was usefully evidentiary, but I didn't think it was absolutely compelling.
1) We cannot know if Adam and Eve suffered Spiritual Death or not, because the acts of touching and eating are not sufficiently separated in time for us to make that determination.
Hmmm.... I don't think I can give you this one.
I submit that, if you can't define the "time-passage" critique from Scripture, then I am unable to consider it a valid critique.
2) We have no record of what would have happened if they had touched but not eaten.
Yes, but we do have the record that while Adam had touched, but not yet eaten, he was not yet Spiritually Dead until after he ate. Thus, we have a Record which fulfills the same function as the hypothetical -- it describes a point in time in which Adam had touched, but had not eaten, and was yet Not Spiritually Dead at that point.
3) This is incidental, but merits consideration: scripture records that their eyes did not open until both of them ate the fruit. Would this not imply a "delay" function, rendering the "touching only" point moot?
It may be "incidental" to this discussion but it's certainly not a "trivial" point by any means! That said, I don't know that the issue is so much the fact that both ate, as the fact that Adam ate -- i.e., not a "delay" function, but a "trigger" function.
That would make this point "incidental" to the Imperfection of Worship discussion, but it does attend to the Nature of Original Sin, which definitely seems to be judged upon Adam's Transgression. At least, that is when the Consequence falls.