Good point on softies & what hurts casinos...
You're touching on something I've believed for a long time, B.P., and something I think many casino owners are missing the boat on big time.
As a prelude, I don't think what I'm about to say applies as much in Reno/Vegas, due to the higher density of advantage players in those cities. That said, however...
I believe, from years of player observation and a keen awareness of if/when/how-good a counter is playing at a table with me, that when a casino limits soft-doubles and hard-doubles on 8 and/or 9, that it ends up hurting the casino in the aggregate.
The reason for softies you already touched on... as a counter's count runs excessively above or below an index threshhold, the increase in the advantage of making the correct play on softies up to A7 occurs on a very gradual slope in comparison to that of a hard double. The reason is because the bigger cards that can hurt the dealer's weak up-cards if drawn work against the player since small cards would help such softies. With hard doubles, big cards both help the player and hurt the dealer so the slope of advantage is much steeper as the count is higher (Don, 'DD and others have a mathmatical term for this "count elasticity" but I can't remember what they call it).
By dis-allowing softies, the house is: 1) Preventing idiots from executing ill-advised softies and.. 2) Preventing players from playing the table due to the rule (by my observation, soft-doubles are the least understood plays by folks who know basic strategy 95% efficiently but they WANT to soft-double and are repulsed by not being able to). When contrasting these 2 points with the "in-elastic" magnitude of advantage afforded the relatively few card-counters of the world, it's clear to me that the house essentially hurts themselves by dis-allowing softies.
By the same token, I often see middling players double a hard 9 against a dealer's 7 or 8 and ploppies sometimes doing it suicidal against 9 or better. When combined with the occasional non-counter who won't play D9 (or especially D10) if anything else (like a DOA shoe) is available, I think the effect of these tightened rules more than compensate for what it gains from the rare counter.
I DON'T believe this to be true for DAS or LS. I think these rules provide more for counters/B.S. players than it takes from ploppies or those who won't play due to these rules.