Personally, I like starting with a clean slate and by that I mean I like taking everything off before I put my work back onto a basement wall. I don't know what your builder put on the wall, maybe something like 1" of polystyrene, but in any case, the old vapour barrier has to come off - you can't have 2 vbs down there.
In your shoes, I would remove the old stuff, put my straight and true stud wall an inch or so away from the concrete wall, put down a roll of 4" wide foam underneath the bottom plate, use the Roxul to fill in the void completely, then staple a 6mil plastic vb
, well taped and sealed with acoustic sealant, right from the bottom plate to the top, not forgetting the spaces between the upper joists. Then cover that with 1/2" drywall...
Remember up here we're in the 'freezing zones' and what we need up here is quite different than what others need in other zones.