Funny that I see this posting. I get sort of the retro look that OP is trying to get in his prints, and he gets the kind of look I want in my prints. I use Portra 160 and 400. I print (like they mentioned in old expired Kodak Supra Endura paper, luster finish I purchased on eBay) it has yellowed but with right filtering you can get right colors, they just look very retro and low contrast. I print at room temp.
I do crave for the high contrast and fine detail, and saturation. I am beginning to try Fuji paper. Perhaps I should try a Fuji Film instead of Portra as well.
The first step is to use fresh paper. If it's still not saturated enough, Ektar is the most saturated negative film I know of on the current market.