I did some work on my daughter's 2007 Prius and when I removed the plastic wheel cover I found aluminum wheels under them. This is the first Prius I've had the pleasure of messing with. Is it typical for Toyota to cover up nice aluminum wheels with wheel covers?
No but it is typical for a Prius. The idea was that they'd save weight by using aluminium with smaller spokes then using plastic to cover those gaps for aerodynamic purposes. On the Gen 2 that you have, they're just a plastic ring on the outer part of the wheel. I see yours has a full cover so that must be an aftermarket one made to look like a Toyota OEM cover (I guess it's fake chrome effect?). On the Gen 3 and 4, it's a full plastic aero cover. There are exceptions. The 2012-2015 Prius Plug-In has normal 15" alloys with no cover and so do the 2010-2015 Prius with 17" alloys. The 2019 FWD XLE have a regular alloy wheel as well (but it is two-tone painted grey/machine finish)