Yes it has this impact/importance. Before we started winning Serie A again we could barely attract any players and we couldn't afford to convince with money otherwise. Jovetic, Cuadrado, Alexis, Van Persie, Aguero, Rossi, etc. how many targets were we unable to get? Our budget grew with our success in Serie A. Getting the top spots qualifies us for the all important CL and winning it get us the prestige needed to be the best. If go a long spell without winning Serie A then we lose ground and the CL becomes even more difficult to attain.
If we have a hard time keeping some top players as it is, imagine if we go back to getting irregular results. We need the prestige, name and money that comes with success in our domestic league to build into a club that challenges for europe every season. We are this now, we shouldn't regress.
Neglecting the platform from which we build on is a sure way to becoming unsustainable at a top european level and jeopardizing the consistency of the club.