I guess I could sorta' see it if you're playing one of those hyperaggressive bless nations that crush the entire map before turn 20 and just outrun your own dominion? I'd rather just take death scales or some heat/cold or... anything but misfortune, really. Seem to recall that some people swear by order/misfortune, but I've tried that and it... doesn't really help. Plus there's some really good beneficial order events.
I'unno, mostly it just seems to add an element of RNG to the game that is incredibly risky. Extra points can give you an edge, obviously enough, but you're counting on the bad events to not be ruinous and, well... putting a(n even) large(r) part of your success in the game in the hands of Dom4's RNG is not exactly what I'd call desirable. It likes to kill people.
An update - sometime in the last month or three, I dunno - changed it so that the effects of order/turmoil on the likelyness of events is pretty damn minuscule. It used to be that you wanted either order/misfortune or turmoil/luck/magic, but now... now the optimal way of doing it is luck+magic and do whatever you want with order/turmoil because it makes no real difference to the other two. I believe its a 12% swing to event chance from max order to max turmoil, who cares about that? Luck + magic is THE strong scale right now IMO. Let's say you have, to pick arbitrary numbers, an 80 gold 7 research mage as your main lab rat. At magic 3 they're at 10 research, which effectively "saves" 35 gold and a little under half a fort turn every recruit, AND about 2.5 gold every turn in upkeep. So it saves you money and fort turns (which are the same thing as money until at least the start of year 3). And then all the gem-gen events will flood you with gems once finish your earlygame expansion and domspread.
All that being said, I ran 2 turmoil 3 misfortune in a game and won, simply by being strong in the early game and running a gold-light build. General rule if you want to take misfortune is, its more annoying than other negative scales would be, but probably less actually harmful. The exceptions are that if you take less than order 2 (I believe) you'll get attacked, any amount of turmoil will make those attacks actually somewhat dangerous, and NEVER take death at 2/3 or drain at 3 if you go into misfortune. I think there's a very strong argument to make that if you go positive on every other non-heat scale going misfortune is an efficient use of points.
You can make them riskier and/or costlier, yes. However, because BV is MR-based, high MR mages and/or those with solid MR gear can largely ignore it, especially if they have high HP and/or regen to make the occasional inevitable failure less disastrous. It's a good counter to hordes of low-cost mages engaging in evo spam, though.
Only if they're not casting high-end evos. A mage casting Fire Storm on a Flagellant zerg with BV is pretty much going to die, even if their MR is 24+. It is highly effective against strategies that are relying on mass destruction battle spells because the type of mages that can tank that are end-game summons; and in an MP game you probably aren't getting access to them if you raced for high-end evos.
The problem with B9 bless isn't its anti-mage effectiveness, it's that it tends to be a big waste of design points: The Pretender buff sucks, it's not a good choice for site searching, and you don't get much in the way of battlefield help from it... all so you can run a one-trick pony strategy based around hoping that most of your army gets killed by the right enemy.
The GOOD thing about BV summons is that it doesn't matter even a tiny bit the actual quality of the sacreds. Those 15 protection 18 defense skill heavy cavalry will be helped exactly as much by BV as a 0 protection 8 defense skill animal summon. There is literally one concern, and that is the HP of the sacred compared to how difficult and costly it is to recruit. This is why LA C'tis LOVES BV, because their Tomb Kings can freespawn two big bags of sacred health every turn totally for free. I've really considered picking up a nation with beefy but useless sacred summons (like MA Tien Chi with their celestial servants) and getting B9, and then putting them second row just as a *hit me you fucker I dare you* in the mid game. Seems like too much of a gimmick rather than an actual useful strategy tho.
I would say BV is at its best for games where you've got a really nice endgame relative to the other nations/players, or where you know it will be decided in the midgame. As E. Albright is suggesting, in the late-late game (or earlier if pretenders are involved) counters WILL emerge. This is true of all sacreds, but BV is best in double/triple blesses and like PrimusRibbus said isn't going to give you many new lategame options seeing as how you can just empower blood into whatever crosspaths you want. I do think that BV is viable but it has a fairly narrow niche, it needs to fit your strategic aims AND you need to be running a nation with a high-health/easy to mass sacred.