Teams in question would be less prestigious than Napoli or Udinese for instance. I'm talking about 2-3 of those that have very little or no business at all to compete in Serie A, except for filling up the quota, like previously Novara, Lecce, Siena regardless of their history. You can probably make a case for any team out there that they have the rightful claim to compete in Serie A, but what what do they bring from financial point of view? Those teams attract relatively small crowd on a match day, not more than 10k averagely, overall they have small fan base, difficulties to find an adequate sponsor or to meet financial obligations... Let's say Juve were to play 4 games less per season, that is in total 5M euros earned less on a match day, surely we can compensate that amount in some other way, but having more time for players to prepare for the European competition and at the same time reducing the risk of injuries, which by the way is significant one considering some of the venues out there, is beneficial, etc..
I'm not advocating the change for the sake of it, but it is rather that I don't see anything valuable that those teams bring to the table, in fact I can see more positives without them; further more I would reduce the number of professional clubs across Italy, because there simply aren't enough funds for that many of them, market is not big enough to support around 90 professional clubs.
The top 7-8 clubs at the moment in case of this kind of change would hardly have any trouble of confirming their Serie A status. I'd say that Juve, Milan, Inter, Napoli, Lazio, Roma, Fiorentina are absolute pillars of this competition, with Parma, Sampdoria, Genoa and Udinese trailing behind, while the others are simply replaceable and their absence won't be missed.
As for the quality it really is a simple; you remove few lesser teams and relative quality of the competition is increased. You can even calculate that one.
