Alright, I know some of you have the itch! I do too, but my wife hates it when I modify her cars. I'm probably going to just end up doing a tint and Xpel paint protection, but it doesn't stop me from looking. I've been searching for the offsets of all the different OEM Pacifica wheels, but haven't been able to find them. I'm thinking it will be an offset +45 for the OEM's. All I know is that the bolt pattern is 5 x 5/127. Don't know center bore (but aftermarkets typically ship with centering rings anyway, info still would be helpful).
I think 20" looks very proportional to the Pacifica; the current Honda Odyssey TE's ship with 18's, which I thought were a little small, especially when you evaluated it against the concept van in 2010. Some Odyssey owners on another forum have bumped up to 20's, which I think look great depending on the style (but that's personal preference anyway).
So naturally, when I'm looking, I already know that the Pacifica looks great with 20's, and then it begs the question, 22's??? LOL!!! In all seriousness, in an aftermarket 20" wheel, probably looking at 8-9" width with an offset range +35-45, +35 and below probably getting a little more aggressive, tire section width 245-265 (have to still look at aspect ratio's to match overall stock diameter). A 22" wheel would probably have the same range offsets, and be in a 8-10" in width range.
Not many online aftermarket wheel retailers have updated their sites. I've been just taking information from various sites and extrapolating. It does look like the older Pacificas (in name only) seem to closely match the current Pacificas for specs. If so, it looks like there are plenty of options out there...