One extra benefit of going nonceless is that it is hugely easier to verify each bet with a script (or verify the script) as there's no history (bet direction, bet size, result) to accumulate, you can just on-demand verify each bet.
Not sure if you're talking about the 2nd method here (nonceless), but i would find this system provably, but not fair. As, it could be possible that the user does not update his client seed while the serverseed will update after every bet. If the operator is unscrupulous, he could take advantage of the users that don't change their client seed as often, and find a serverseed pair that will have an advantage, assuming that the user does not change his betting % or hi/lo option.
of course this would require some work on the operator's part as well as some added technical knowhow, but i could see something like this being done.