Right none of those tricks would work against an 8 INT Orc, a 1st level thief or a commoner.
No trick automatically works against anyone as a simple matter of fairness and consistency. 8 INT isn't all that stupid. I've known plenty of people with around that intelligence IRL. They get by. Assigned to guard something like a gate, they are at least going to spare an action investigating what's up. Bored, they'll try to strike up a conversation. Ignored, they'll become angry. Seeing a stranger, they'll at least want an introduction. It's not like all orcs are one big happy family, after all. Seeing prisoners, they may desire a bit of sport cruelly teasing them. With little skill and a lack of notable wisdom, they should be easy to trick but the point is - you have to actually trick them. You can't just assume that your plan is going to go off without a hitch because 'magic'. Almost no plan ever does, magic or otherwise, and the sorts of things I've suggested aren't exactly the sort of things that a plan of this sort should overlook or find surprising. If, "Ooops, I didn't consider that the orc guard might actually act like a guard and want to converse with me.", is your idea of, "your creativity", then may I suggest that that word may not mean what you think it means.
Let's not that the 1st level Orc automatically gets a saving throw to penetrate 5e Disguise Self if he takes an action to investigate you. Sure. He's not that bright. He may fail. But the point is, you still got to pull it off.
Even a 1st level commoner - or 1st level warrior more likely from his job - is a person with a brain and a will - even if you've partially stolen it. And in 5e, let's note that Charm Person gives no other benefit beyond the guard sees you as a friendly acquaintance. It gives no bonus to persuasion or deception nor allows you to suggest any course of action. At best, it belays hostility unless you do something to provoke it. It's not reasonable to suggest that the friendly acquaintance begrudgingly lets someone who is a mere friendly acquaintance escape from jail with a bunch of people he doesn't like, knowing that he's himself is likely to be executed if he's discovered to have abetted the break out. That's not a sacrifice even stupid people make for mere acquaintances.
As for your assertion that a 1st level thief has stolen the princess successfully and is bargaining to obtain the Holy Scepter of Bobbybob, well, I find that to be a rather self-serving reinvention of the narrative. I might believe the 1st level thief evil villain has stolen the swineherd's daughter, and is ransoming her for a purse of gold, and perhaps he'll be momentarily swindled by the sight of your illusionary gold - at least long enough to release the swineherd's daughter. After all, he may fail his investigation check to detect the illusion when he gets a chance to observe it. But even a moron is going to quickly realize your purse containing only a minor illusion is empty of any tangible thing, has no weight save for that of an empty purse, and at the very least is entitled to realize that its an illusion - per the letter of the rules - as soon as he reaches to touch his coins. So, frankly, you aren't going to fool even Tad the Slow-Witted brute for very long, much less someone of sufficient intelligence to plot the kidnapping of the princess and plan to acquire a relic and who is probably accustomed to cheats and plans for them as a master of course because deception is what he does. You think people who demand ransoms don't count the money before they release the hostage?
One point of all this, regardless of the edition we are playing, is to allow for actual creativity and planning to work instead of treating spells like a win button. Another point of this is to ensure that characters that have invested resources in being skillful, aren't trivially outdone by the merest application of magic. In short, it's just basic fairness in your judging as a DM.