Showboat is a no go for me. It's just a morale based VA that does nothing unless you pancake your opponent. That makes it limited in both effect and power.
If you use a lot of rushing plays that call for an O-lineman to "pull" then I would highly suggest Pulling Lineman (I use it).
If you DO pass from time to time, Pass Blocker is another good one to get.
Downfield blocker and Outside Blocker is good for TE's and WR's because they're more likely to have it trigger than O-line will. BFB's... hmmm... I think it'd be good but there are other VA's they should likely have 1st so I would guess they don't get either of those VA's but, if you had to choose one for a BFB, I would go with Downfield over Outside. Likely more useful of the two.
I use to love Stonewall... then hate it... now I believe it's good for pass blocking (not so much good for run blocking) as it stops some of that 'pocket collapse' and buys a bit more QB time.
Uh... Wise? AOI is an SA, brother... and that's a different argument.
But you're right. And it's why Showboat is kinda obsolete.
If you're not adding one of those VA's I listed above then Wise is also right in picking a 'Skill Boosting' VA although I usually go for one that helps cover/enhance a skill I feel needs it most. More Strength is always good... Agility as well... even Blocking. But don't forget Vision which, even for a rushing team, should likely be around 60 (with all VA and EQ help applied). IMHO.