For the 50nl hand, since he's on a shortstack I'm guessing he's not a regular and if he had AA or KK he would never have flatted that raise preflop.
I'm going to disagree with this statement. I find that short buyers frequently like to slowplay so they can get all their chips in when they have AA or KK. I think limp-reraise is more common, but I think they do limp-call strong (unless you have stats to show a loose VPIP). Nevertheless, you do have KK, so I'm not sure it matters much.
I do agree with the overall sentiment that the first hand is a shove and the second hand should be played more gingerly (with position, yay!).
In general, I'm more inclined to like our spot in the first hand but not like it in the second. Part of the reason is that we beat more hands in the first case (there are plenty of overpairs in hand #2). The other main reason is the reverse implied odds
. In the first hand, the money left behind is insignificant, so it's really just a decision of whether you think you have the best hand now (which I think you do). In the second hand, you stand to lose a lot of extra money if you're wrong, and you won't win much extra if you're right. That is not to say I advocate folding, but I'd exercise pot control. I'd play position, call off bluffs if non-scare cards come, and probably fold if scare cards do come.