I started to reply to this last night before a lot of these comments had been made, got distracted and now there's lots of other commentary.
We made a tube bumper to replace our stock bumper. One of our main reasons was the stock bumpers can barley stop a mosquito. It's actually tighter to the body than the stock bumper.
I believe the early E30's had pretty good bumpers to start with. So you can probably just make some improvements to the stock ones and be in good shape.
Here are some suggestions:
Fix, delete, weld the stock mounts if they are shock mounts so it is solid mounted.
(See LTD Scotts post, may not be a good idea)
The most important thing to me would be to make sure the ends of the bumpers are supported and smoothly flow into the body. The early E30 has big plastic/rubbery bumper fillers between the bumper and the body. It looks nice and all but doesn't do much. If you have any contact up in the front, the ends of your bumpers may get hung up on another car. If this happens, it will probably cause both cars more trouble than the bumper may have helped. So making sure the ends of your bumpers don't hook stuff is a good idea.
A friend of mine backed out of a parking garage in an E36, caught a pole which snagged the inner bumper though the plastic and it pulled the front of the car out a good ways.
Troy
#35 LRE
1973 Datsun 240Z