Some more comments
Hermione's comment on the blood status of DEs: By the time she made it (during HBP) she knew the names of some 17 of them. She may have done the research and found irregularities in a couple of the family trees.
Slughorn's attitude in 1996 was very significantly influenced by not wanting to be associated with known DEs. He asked about Theodore Nott, but when he learned that his father was among the DEs arrested at the Ministry he did not invite him. But he didn't invite other Slytherins instead. No members of influential families in Slytherin in the year above or below Harry's?
On wealth and brooms: For whatever reason when Harry managed to end up with a more modern and superior broom than Draco's, Draco did not get an upgraded one. Either the Malfoy fortune was being overly stretched by donations and bribes or Lucius had other priorities.
Slughorn's attitude in 1996 was very significantly influenced by not wanting to be associated with known DEs. He asked about Theodore Nott, but when he learned that his father was among the DEs arrested at the Ministry he did not invite him. But he didn't invite other Slytherins instead. No members of influential families in Slytherin in the year above or below Harry's?
On wealth and brooms: For whatever reason when Harry managed to end up with a more modern and superior broom than Draco's, Draco did not get an upgraded one. Either the Malfoy fortune was being overly stretched by donations and bribes or Lucius had other priorities.