I would never buy a house with aluminum wiring for anything other than service cable or wiring to 220V appliances. I've seen too many homes with aluminum wiring where plugs, light switches or fixtures were swapped out for fixtures that were not rated for use with aluminum wiring. I picked up a FLIR camera that attached to my iPhone - was at a friends house that had aluminum wiring. Was screwing around with the camera and noticed some hot spots on some walls - looked closer and they were outlets. Felt the outlet and it was warm to the touch. Killed power to the circuit, popped the outlet out of the wall and the terminals were crispy critters! Freaked my friend out a little - swept the rest of the house and ended up replacing a dozen outlets, a handful of switches and checking every ceiling and wall mounted fixture. What a nightmare - many of the hot products showed obvious signs of overheating.
If handled properly aluminum wiring can be effective. The problem is it's often not handled correctly :(
My understanding is that Al wiring can be cheaper, but specifically in the housing domain, because virtually every fixture is copper based, it ends up being a huge PITA.
Aluminum for wiring works just fine if properly engineered and can be cheaper once that engineering is amortized.