Eh. I feel like sandbox games need their limits in order to have fun. A gaming memory that begins "I accidentally stole an armored van, ditched in the lake, hid in a hat store for four minutes on low health, and stole a helicopter as a getaway and got some health" is a lot more fondly remembered than "I meleed a police car to explosion and shot everyone after that".
Saints Row the Third, for example, gets horribly boring when you level up all your resistances and abilities. No damage from bullets, no damage from vehicles, never reload, infinite ammo, no damage or ragdoll from explosives... nothing can kill you except destroying a vehicle you're driving. It's just so boring. Standing in the middle of a road and constantly firing the default pistols -- because when upgraded they quickly shoot explosive ammo that kills freaking everything at perfect accuracy -- that shit is boring. Having high speed chases where your coop buddy desperately weaves around police cars while you shoot your last RPG shot to knock off an armored van -- that shit is fun and memorable.
So, nothing really is fun with cheats for me. I'd just play on Easy mode and get the experience I want.