6D, S17, 75% pen, 1-10 spread - 50 million hand sim
always hit soft 18 vs 9,T, hit soft 18 vs A TC<+1
WinRate 1.99 IBA .933
always stand S18 vs 9,T,A
WinRate 1.94 IBA .911
I personally think the index play of standing on soft 18 vs A at TC +1 is a good one to incorporate into your play. It isn't going to make you much money, due to the infrequency with which it occurs. However, the rare times that you end up with an A7 vs a dealer A with a big bet out, take insurance, the dealer doesn't have BJ, then you proceed to hit your hand, you've just waved a giant banner saying that you are a sharp player. Maybe nobody is looking, but if someone does happen to be scrutinizing your play at the time, you are really exposed. Standing on soft 18 vs A at this time has the double effect of providing cover, and being the correct play given the count.
Note that standing on soft 18 vs A at TC +1 only applies to an S17 game. Always hit in an H17 game.
Incidentally, this is one of the commonly recommended cover plays which doesn't become more correct as the count gets higher. (for soft 18 vs 9,T at least ... which combined occur 5 times more frequently than soft 18 vs A). Other cover plays such as always standing on 16vT/12v3/12v2, or doubling 11vA, 8v6, 9v2 become correct plays when the big bets hit the felt. As such, these other plays have a very small effect on a player who is aggressively wonging. The opposite is true for always standing on soft 18 vs 9,T,A. As such, you may want to consider abandoning the cover when the situation comes up with a big bet out.