I don't think cheats make it any more fun, I never use cheats.
It actually does. Well, for me anyway.
Cheats in Saints Row 2 aren't just the usual invincibility and such; they change the physics, how civilians act, and a bunch of other things, too.
Whenever I get bored in SR2, I enable the "evil cars" cheat, "zero gravity" cheat, and some other cheat that makes it so you can plow through cars without slowing down. Anyway, it's real fun trying to avoid getting hit by the cars and flying into the sky.
In fact since the code is shared between them so closely during development there was a bug that caused the EDF from RF:G to invade SR2.
That's strange, because RF:G was released about 8 months after SR2. Are you sure you're not talking about the EDF costume and vehicles in one of the SR2 DLC packs?