Your problem look similar to my old one. I bought a set of rims from a 1991 Honda Accord EX, which were/are in pretty bad condition. I don't know how much it will help you though, because I wasn't worried about stripping/damaging the clearcoat as I'm planning on stripping it later anyway. Anyway, here's my process, hope it helps
1- Washed with Dawn and a scrubbing brush to get off as much surface grime as I could
2- Megs Hot Rims, let it sit for a little while, rinsed thoroughly
3- Turtle Wax Bug and Tar remover, I let it dwel for a long time. I only used this stuff because I had it laying around and it wasn't getting used. I put it in an old empty bottle of EO AWATC to apply it evenly(worked well to get thin, even coats)
4- EO AWATC + toothbrush to get into nooks and crannys, and remove huge chunks stuck on the inner rim.
5- Megs Hot Rims + toothbrush on corners, stubborn areas, etc.
5- EO AWATC + 0000 steel wool, worked pretty well for those tough to reach areas, probably could have used an even tougher grade as this didn't remove everything.
I noticed a dramatic improvement, especially on the inner side of the rim. This did not make it 100% better by any stretch however.
It's important to note that these rims cost $50 and that I was not worried about harming the clearcoat because I was planning on stripping it anyway I'm not saying to go do this on a set of $4,000 dubs or anything, or that it is safe to do.
Here are some before/afters
Again, not 100%, but it's a start. Good luck:xyzthumbs