Mark,
I see where you're coming from. I've had a lot of discussions over the use of a BOV on my engine. BTR Preparations have commented on it and I also note that Julian Edgar in his 21st Century Performance book actually questions the use of BOV's. I also believe that Cossies dont run BOV's, or at least not the high power ones. At the end of the day its how the car was sold to me, so if the turbo fails it should be a warranty issue! The car certainly felt much quicker through the gears. I'm actually going to try using the Seconmdary Air Supply valve as a dump valve this weekend, as this is originally where my BOV was venting to, not that the SAS valve is operative often - well mine wasnt when i monitored it.
Peely, all I can suggest is that you try it. You might get away with just removing the vacuum feed to the BOV, though the boost pressure might start to open it, just reverse it if that happens. One day of careful driving isnt going to hurt the engine and if you arent happy with the results go back to original. If you do remove the vacuum line to the BOV remember to block it up or the engine will try to breath through it.