But I believe (untested) that same-type challenging is crucial to the endgame. In the middle game, you have two tasks: Get points with smaller sneaks and challenges, and build your one true magnificent flaunt for the endgame. That flaunt can be even of a weaker type because the rule of same-type challenging protects it. It introduces a separate direction of hand management into Sneak.
This is what I'm not sure about. I have only played it with the same-type challenging, I think it would be interesting to see if/how the dynamics change without it. I don't see any clear argument in favor or against it.
The main reason I suggested trying to cut it was to simplify a game while cutting a mechanic what I perceived to be weak (at least mid-game).
And this build-up of tension -- you have exactly one flaunt during the game, at the very end -- goes in a great way with your proposed cut of mid-game flaunting for simplicity. It sounds wonderful on paper.
Downside: Same-type challenging is a special rule only for the very end, with unclear purpose. If somebody happens to make the same type of combination, you're hosed while everybody else's flaunt stands. That will feel random. If we remove the restriction of same-type challenging, more people get hosed. It will still feel random; will it feel better?
That's not really how it works in practice. Why would you build up to a big flaunt? You're better off using your good cards to catch a sneak (or at least sneak in the hope of catching someone else's cards), rather than just bringing them home. This is what happened in practice: good stuff was played to sneak or catch sneaks, while at the end the flaunts were just cobbled together with what was left. Unless you reward the flaunting at the end (everybody flaunts and the same time and the winner takes it all?), I don't see what you described happening at all.
Worthless leftover cards seem like the cleanest design, both for easy bookkeeping and to avoid extra rules like no-undercutting. I really want to make that work. I'm open to switching to negative points when worthless cards don't produce the desired strategic late-game decisisons.
Negative points for leftover cards was probably the single most significant rule change, and affected the whole dynamics near the end of the game. Our games were too close anyway to compare stacks by height, so you had to count. But we just removed the same amount from our point stack and then counted. Most played had nothing left anyway, I don't remember if anyone ever had more than 2 cards left. I think the negative points at the end are quite natural (and similarly the no undercutting rule), and adds barely any complexity. I don't think it's unelegant. It brings a great improvement to the game dynamics at (in my opinion) pretty much no cost.
I really found it interesting how the dynamics change as the game progresses, pretty easy-going at the beginning, people get more agressive as the game progresses, some exciting maneuvres as the pile draws to an end, and completely different dynamics in the final round. I don't see this happening if remaining cards don't score negative. The pressure to get rid of cards really adds to the later game.
After the rounds from the last days, the cutting of flaunting discussed above is really the only change I can think of at this point that seems promising (but for the reduction of complexity, I don't expect much of an impact on the game dynamics).