[weby]

Brown dwarves are.. interestingly boring stellar objects.

Young Brown dwarves can indeed have high luminosity and temperature, but once they have stopped fusing hydrogen that is likely not the case any more.

And as to how many there are in the universe compared to other stars.. no one knows as the detection distances for them are so much lower.

As for attractiveness of systems: I would definitely give a lower modifier for low water/low gas giant type systems. How much lower depends a lot of your choice of technologies. If you have Traveller jump drives that require hydrogen or your normal space drives require such then the lack/rarity of such will be a big modifier, if not then a small one.

Further the total mass of a system with just a brown dwarf is likely a lot less, meaning that it would likely not attract as many other planets/other objects. It is much closer to something like the Jupiter surroundings than the full Solar system. Thus I would reduce the objects around such compared to a normal star system. (With the exception things like "almost binary star systems" where one of the objects made it to brown dwarf and the other is just a gas giant type object... )