I have tried everything on both my speedmaster, who's engine is the same black textured paint as the storm, and my Tbird with the same also tho chrome side covers. the best thing i have found to make it look new and resist further dirt adhesion is called Maxima SC-1 clear coat. It's a silicone based product and it works fantastic on the entire bike even the tank and chrome. (tho if yours has the flat black tank i wouldn't use it there)
That said, for real tough dirt i'd use a dedicated cleaner first and simple green works great. But no cleaner that cleans very tough dirt is also going to leave it looking great and leave a protective coat. (and SG removes dirt great but leave the finish looking dull, so you must then use a finish product) So SC-1 is what i use for that. I DO used it as a one step cleaner/finish too, but thats because my bike never gets super dirty in the area i live. SC-1 is the best thing i have used so far, and if you use it on the entire bike the finished look is shinier and deeper than anything including all waxes and other sprays. It's really that good. I don't use anything else anymore. Occasionally i'll wax it, but i'm really not sure i need to even do that anymore.
Anyways, that said, the main reason i bought it several years ago was for the black engine parts because thats what it did best. But they recently improved the formula and thats when i found it works amazing on the whole bike where as before it was too hard to remove from tank and fenders because it would leave streaks. Now it works better than anything on all paint and even chrome. The look it gives to my tank and fenders is truly deeper and shinier than anything i've used, and i'm a detailing junkie. Only issue is, can you find it in aus? I know some people have had problems with some detailing products being impossible to get in some countries due to environmental laws.