My solution has been to buy a new bike for the wife when I want a new one as well. Hasn't been a perfect solution but she rides and is more amenable to my shopping.
Personally I have never been impressed with aluminum road bikes, I've ridden a number of them and they're nice enough, brands like Cannondale can make them really lively and comfortable, trek and specialized aluminum to me is kinda whatever. This is regarding road bikes, my mtbs have almost all been aluminum and I can't complain there. Carbon from trek though has always been a really nice ride and way better than their aluminum, and I would consider it worth the cost difference on a road or endurance bike over their aluminum. That said, if I was spending enough to go that route, I'd also look at higher end steel or titanium instead which I like better. My current road bike is carbon and I absolutely love it, but it was on clearance and if I had to pay the full price knowing how well it rides, I'd still have gone Ti.