Somewhere in amongst the "he's not that good", "take the money", "Argyle price" - you have to factor in the player himself, if (and its a big if) if an established Championship Club has shown an interest, he would rightly want to move on for his own gain, that has to be expected when you are in League 2.
He has 12 months left on his contract, we price him out of a move, he can sulk, do the bare minimum and move in January for far less and everyone loses.
I dont think he has the ability to step up to Championship level, however, i think i'd put a clause in any sale for 15% for any future sales, just in case. We have seen over the years even at that level clubs spend big 7 figure sums on average players out of desperation.
Let him go, add the money to RL's budget and move on.