I never had bolt ins, but the argument against them is that the bolts stretch enough that they jsut arent' effective. There was nothing to relocate for the BMR install. Unless you have a driveshaft loop or intrusive exhuast you shouldn't have to relocate anything for DD either based on my cousins car which i didn't actually do the install on but have spent my time under.

 

I think it's worth it. I like the difference it made in the way the car steers through corners. And it's not a real expensive part.
You also might consider a stiffer front sway bar.
As far as bolt in vs. weld in SFCs I think the drawbacks of bolt in SFCs are mainly at the rear where (I believe) the only attaching point is the LCA pivot bolt. That would not only significantly reduce the effectiveness of the SFC but possibly have negative effects on the rear suspension action. But I would expect that DD type SFCs along with a stiffer tunnel brace would stiffen the floorpan considerably more than the other type.

 

Thanks, the BMR SFC's are my next thing to do. Lucky I have acess to a shop with free lifts and a free welder!