I like the idea that a failed roll means your preparations are at an end. It's a simple consequence that's reasonably easy to handle. It also keeps the stealth threshold low (maybe?) so the player wouldn't have 50 stealth points, but is more likely to have 2-10 dependent on what the character's ability is like you're saying.
My problem with that is when the number is not maxed out, the player may just try to abort and come back another day. Okay that might be realistic but it could chew up time at the table not to mention time in game. Each time the player doesn't get what they would consider an optimum result they would just abort at the planning stage. I think some of the fun of this would be a player trying to manage under a small number of points.
Obviously there could be the story driven "There's no time, we have to go in now!" but that would get old for the players really fast.
Maybe if the results of the rolls were described differently? Instead of "You don't see anything more." when doing your surveillance and prep work, to an assurance "There is nothing more." there'd be a better player reaction? So you can't come back tomorrow and try again. The results now are fixed. That seems a bit weird though because it's based on the PC's skill.
I'm not sure about the push your luck mechanic because it would tend to leave the PC with no SP (Stealth Points) and thus defeat the point of having them in the first place.
What if each failure roll gave the player a condition where their surveillance or preparation has holes? This would be triggered at certain SP levels. For example, if I failed my second roll, my second point has a hole in it. If i fail my eighth roll then my eighth point has a hole in it. If I have to use those points, I have to do something risky or maybe hide myself fully to stay unnoticed.
I don't know, I'll work on it.