Reverse Engineering Course: https://news.ycombinator.com/item?id=22061842
Reverse Engineering For Beginners: https://news.ycombinator.com/item?id=21640669
Introduction to reverse engineering for beginners: https://news.ycombinator.com/item?id=16104958
A lot of the reverse engineers I know seemingly have deep platform knowledge and can do things like cite Win32 docs from memory.
Both when looking at a particular problem, but also in sticking to RE in general for long enough to pick up the skills and tricks that make you quick. There are countless tricks you pick up that cleave off huge amounts of time that would otherwise be wasted.
It won't help you with PowerPC, but the chapter list is: x86 and x64, ARM, The Windows Kernel, Debugging and Automation, and Obfuscation.
The book was written in 2014, so it should be reasonably relevant for modern purposes, and especially so if digging into any software older than 2014.