Absolutely he can improve the program even more.
A lot hangs on the success of this new recruiting class and the older statesmen coming back, but Collins has been turning NU into a respectable program, and all the interviews and 'The Journey' stuff is big (haha) PR about a coach that respects, loves, and fights for his players and his players reciprocating. That kind of stuff could turn NU into a primary destination for the kinds of players he wants.
I think Collins has his eyes set on a championship, and I think that barring the injury bug he has had a couple of teams in the last two years that were at least sweet sixteen material - and I think he knows it. He wants more, and he can get it at NU even with its baggage.