The Italians prevailed 13-6 over Scotland in Rome to avoid a fifth consecutive wooden spoon.
It was also Brunel's first success in charge of the Azzurri.
"It's difficult but I truly believe that we have the capacity to win this tournament in three or four years' time," Brunel said.
"The international level is very high.
"From here until the next Six Nations, we have six games and we have to progress a lot to achieve the level that we want to be at.
"In this year's edition, we have seen six or seven new players with respect to the old guard and I believe that during the summer, this group will keep on growing."
One of those players was Aironi centre Giovambattista Venditti, who scored the only try against the Scots.
Italy have yet to find a balance in their play.
The Azzurri lost their opener 30-12 in France but did push England very close before falling in that game, 19-15.
Defeats to Ireland and Wales were next.
"There have been games where our attack has done well and our defence has not and vice versa as was the case against Wales," Brunel said.
"We played a great opening half against Ireland but we weren't able to keep it going in the second half.
"Against France we tried to impose our play."
At least the Italians ended their campaign with a victory at the Stadio Olimpico.
"I think what we have to do is take all the positives from every game we have played and put it together," he said.
"Only like that will we be able to build a winning side.
"We have grown week by week and made less mistakes as the tournament progressed.
"There are margins for improvement and there is a good base for the future.
"Right now, we don't have the capacity to impose our play for 80 minutes but against Scotland we were on the right path.
"We will continue to grow if we work like we are doing."
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