If you happen to be doing any graphics hacking for Saturn games, remember one thing in particular -- Sega developers used Motorola (Big Endian order) format for palette data, whereas PlayStation developers used Little Endian format. That's the way it works in Dragon Force, anyway.

It does if you need to make ASM hacks (like change the font size, move windows, compression, etc.). 

This is a rather uneducated guess, but the difficulty your hear about is probably more about the efforts one needed to make to utilize the power of the two main cpus (instead of one), rather than about the SH-2 language itself.

I'm not very experienced in Saturn hacks (only ripped some GFX for Dracula X), but the Psx is really easy to hack (a lot more than old bags like the Snes) and the processor is seriously neat to work with (can take care of Snes like VWF without any lag problem). We have 3 emulator with debugging features (PCSX Agemo, PCSX Debugger, and pSX), and IDA is a great help when it comes to code disassembly. There is only one problem: no decent assembler. We have Spasm, but it sucks and you need to create an .asm file because it can't work with multiple org directives. Also it can't reinsert assemblies directly into files, so you have to paste them manually or use a batch program to do that automatically.

You don't have to recompile the whole thing, especially considering that some games don't even care about the CD Toc and use a custom format for locating files, so you can just throw the expended files wherever you want and let the game do the rest. And even if the game uses the CD Toc, you can always change lba and size values to point to a new area of the CD and you wouldn't need to recompile the ISO at all. Even if Cless updated his doc, it doesn't mean it contains all the procedures to work on a Psx game. That doc is probably 1/20 of the actual Psx hacker bible.

Read better my answer. I know what XA sectors are, and you can live without touching them at all. Again: ISO recompilation is NOT necessary.

I told you that already: if the game uses the CD Toc, update those sectors (Winhex works fine here) so that the file is located at the end of the ISO or anywhere else you want it to be, then reinsert there your new file with CD Mage or whatever you prefer. If the game uses a custom toc, do the same as before but update the game internal toc instead of the cd's.