Jack, I find that when you mix Vitalin it initially seems dead dry, then before you know it, a bit more water turns it into what loooks like a stodgy mess. I think its because the constituents absorb water at different rates mate, and if am not mistaken many anglers mix/wet it before hand.
Its whetever you feel confident with! If its like putty that sounds ok for the centre of the method feeder, as you dont necessarily want this part to break up.
I mix it up until its dry and crumbly, then separate some off for the centre of my feeder and make this more sticky and thicker, the bit for the outside being a bit more crumbly which will break away leaving my hookbait exposed!
Your right about the treacle but molasses is a lot cheaper,if you get it from an animal suppliers about ?4 a gallon.