Well from heaps of riding them roads, I would suggest if you want to get the most out of it and have something to talk about, I'd do the whole trip at least to Townsville via the inland route Link:
http://goo.gl/maps/yjpQI work up North at the mines and that inland route just has heaps to see if you take the time too look.
As for the roads, well they have pot holes and maybe some dirt, but who cares as you rides to what the road is. Oh yeah theirs Road Trains and cockys in all kinds of tractors with gear on behind and heaps of fools and critters to hit but that all part of the deal?
That road from Townsville to Cairns is just like out of a postcard and I always try and make Cardwell, maybe half way between Townsville and Cairns for Breakfast as I just dig sitting on the jetty looking out over the islands

Cairns sucks and we'll leave it at that.
The ride back on the Bruce hyway to Brisbane is not a problem no matter how fast or slow you do it. Could probably stop off at Bundaburg to see how they make the rum and their a few other detours like that as well. Oh yeah, on the way back when you get around Byron Bay head over the hills to tenterfield, just a bloody good bit of road and when you get their you can drop into the Saddelery shop that peter Allan bloke sang about.
Forgot to say that out West and up North this time of year you could freeze the proverbials off but during the day maybe only a jumper on under the jacket should do.