I've owned cars with and without alloy wheels and never been able to detect any difference in performance due to them. There are distinct disadvantages of them, however.
They are expensive and easily stolen from an unattended car so you need special nuts to protect them. This is nuisance when you need new brakes or tyres, and you are in trouble if you lose the key-nut to remove them
They are easily damaged, if you curb them, and you'll either have to buy a new wheel or more likely a new set of four, or steal one, or get them refurbished at huge expense and inconvenience.
I have a friend who managed to hit a pot-hole which actually cracked the alloy wheel as well as writing off the tyre. That might have cost him a new steel wheel - it would have buckled rather than cracking however - but it would not have been anything like teh cost of a new alloy wheel
Being anodised, they are subject to damage from flying stones and gravel and if you suffer this it looks terrible.
I think steel wheels with hubcaps which you can replace, are a much better solution. Alloy wheels are a pure vanity project. That said I have two cars both with alloy wheels. I like the cars, for other reasons and the bloody alloy wheel came as part of the deal. I would have preferred the same car at a lower price with steel ones.