Mileage is unknown, these came with the car. Date codes are 16 and 17, so not too old. They're certainly a little crispy but the car was running well. No apparent issues even under boost. I have been trying to minimize a ~2200 RPM misfire under low load but I think I have that knocked out with additional ignition advance.
In the past I just replaced these routinely because they were relatively inexpensive and I didn't think twice. Never really had a bad cap or rotor. Can we tell much about them just by looking?
They do look a bit crusty.
It is perfectly fine to scrape the contacts clean: a sharp tool or a Dremel with a brass brush should leave the cap & rotor working like new. I've fixed misfires this way.
Also I used to replace them fairly frequently, but they are getting pricey these days (at least the l-jet ones), so unless the carbon contact or the plastic fail, I'll keep restoring them.
OE ones on high mileage cars that I have seen never looked that bad on the models that had them. It looks like there is a lot of arcing between the contacts. Possible someone filed the rotor to much (does not look it in the picture). Poorer quality parts could be the problem as the gap between rotor and cap contact is to great causing a gap which the current is arcing across.
I would replace them if possible with Bosch as they are the ones that I have seen before that last.
Problem is now all parts are of a lower quality including the OE parts
It does run better with a fresh cap and rotor. Most noticeably in the lower manifold pressure areas, such as when lifting off the throttle before an upshift or cruising at moderate speeds. Can't tell if it's different under boost but it might be a little better. Hauled ass before, still does.
I went with Bremi components. Bosch hasn't been good since it was made in Germany. Most of their components are "globally sourced" so you can be certain they are made where it is cheapest. Bremi is still made in Germany as of the time my parts were purchased.
Bosch was the original for the cap and rotor. Beru made most of the the ignition leads. Resistors Bosch or Beru. Later e34 on Bremi was more evident for ignition parts. At the time what was available was the BMW original brand or the same item in the makers box. Once the cars became older models then there were more options as other brands made replacement parts.
In Europe cost for the cap
Bosch €120
Beru €75
Bremi €58
Cheapest is Maxgear at €42
