Who actually gets added
Expansion is usually argued for on behalf of unlucky teams, but the places tend to go to sides with mediocre resumes from strong conferences. The romantic case is made for one type of team and the benefit accrues to another, which is worth noticing before endorsing the principle.
The regular season pays
Every added place reduces the stakes of the months preceding it. If nearly everyone qualifies, the games that currently decide qualification stop mattering. That is a real cost paid quietly across an entire season to gain a few days of extra content.
What makes it work now
The tournament's grip comes from a hard boundary and a format where anyone inside it can win. Widening the boundary weakens the first without improving the second. I would leave it alone, and I would rather that argument be made about meaning than about tradition.