Rossi, who will leave the Italian team at the end of the year to return to Yamaha, claimed just his third podium for Ducati when he took second place at the San Marino Grand Prix a fortnight ago.
The nine-time world champion has been bedevilled by his Desmosedici's inability to preserve its tyres during the latter stages of a race, but that problem appeared to be cured as Rossi showed consistent pace on his way to the runners-up spot.
Rossi and team-mate Nicky Hayden also enjoyed a productive test at Misano the day after the race, but knows proof of an upturn in Ducati's fortunes will only become evident this weekend.
"We come to Aragon with a positive outlook after the Misano result, even if we also know that every race has its own story," he said.
"It will be our first chance to check if the progress we've made will also be confirmed at this track, which is very different from Misano.
"It's fast and challenging, and managing the tyres at lean angle is very important.
"Concerning that, during the test after the last race, we tried a swingarm that I liked as it provides a bit more grip with the bike leaned over and stresses the tyres less.
"Anyway, we'll see. It will be a chance to understand if we've really improved."
Rossi's second place was down in part to a nightmare race day for title contender Dani Pedrosa.
The Repsol Honda rider had qualified on pole, but a problem on the grid forced him to start at the back, before being collected by Hector Barbera halfway round the opening lap.
The DNF drops Pedrosa 38 points behind Misano winner and points leader Jorge Lorenzo with just five races remaining.
And Pedrosa knows he must bounce back immediately if he is to haul in his Yamaha rival.
"The bike is working well and I'm feeling good; we go there with the same determination as always and motivated to continue riding well and have another good race," he said.