How far you driving?
I've been a long time fan of Dalby but went up last weekend and almost died of boredom. Only did the new red from the visitor centre to Dixons Hollow but there seems to be very little flow in the trail (the first descent after Go-Ape does actually go down but you feel knackered by the end of it because of all the little rise and falls). There is work going on with some sections to just flatten the trail off, making it feel like more of a footpath than a red graded bike trail – theres even one section just before Dixons Hollow which used to be alright – no flow at all but rocky and made you think (a little) – theres now a completely flat bypass to the first bit – its like a blue/green option on a red graded trail.
Didn't bother with the rest, just sacked it off and took fire-roads back apart from one bit of the old red which was excellent. Au natural almost.
Like I said, used to love it but it sent me to sleep. Trail centres are meant to offer a decent alternative to natural riding – offer more bang for your buck but I believe there is MUCH better natural riding within easy range of Dalby.
In terms of your other questions, yep – sometimes theres LOADS of ice. We used to ride it the day after boxing day every year.
Don't think you can park up and not leave – there aren't any showers I'm aware of either. There is a camp site at the entrance to Dalby and one just after the visitor centre though.