Well worth a visit for sure - I've been there a couple of years ago during the Christmas holidays; I've yet to hear of someone, regardless of not being an Alfista or not even a car enthusiast, not enjoying the visit.
During my own tour there were people from all over the world - those who spoke languages I could understand, I heard making plenty of enthusiastic comments. Runaway favourite was the racecar section - people looking at the 1950s F1 cars and realizing how absurdly bonkers these were; Also, most of the cars were actually raced - they still bear the marks of their on-track adventures - the touring cars, I'd say unsurprisingly, being the most beaten up
The taxi driver who took me to the museum from Malpensa...had never been there, notwithstanding the fact he spoke with the thickest Milanese accent I've ever heard.
As for the shopping centre, it's relatively new - I think it was opened a couple of years ago max; It has the first Primark/Penneys in Italy. Unfortunately, when I spoke about being to Arese to a bunch of friends in Italy - some of which LIVE in Milan - they all went "ah you went to the new shopping center?". FFS.