After watching team-mate Lance Stroll enjoy an upgraded aerodynamic package last weekend, the four-time champion made the most of the new parts on Friday and finished eighth and 11th in the two Friday practice sessions.
"I think it is fair to say it was our best Friday," said Vettel. "I was happier with the car.
"Obviously, it is a different track and different conditions but generally, I felt a lot more at home. It seems to have improved.
"It is very tight and it is hard to say where we are going to be tomorrow. I think we need to look overnight at what else we can find and hopefully we can squeeze a couple of extra tenths."
Vettel has struggled to gain confidence with the car since moving from Ferrari to Aston Martin during the winter but asked if he could feel the benefit of the upgrades, the German replied: "Absolutely, I think it is a step forward.
"It is good to tick that off and now we have to try and improve the package, where we are now.
"The midfield is very tight so anything we can find will work in our favour. It is a long race as well, tough on the tyres so lots of things to look for."
Vettel reached Q3 last weekend for the first time since last season's British Grand Prix and believes he has the chance to repeat his performance in Spain.
"I think that is the region we are targeting for and if everything goes well, we will be in that region," he added.
"It is going to be very tight, there is a lot of cars fighting for these spots. We just look at ourselves and what we can do better and then that is maximising our chance for Q3."
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