If the apps are qualitatively good enough and suit my needs, yes, I still buy. GPS apps are always a good investment.
Paid apps that I find the least interesting to buy are apps that rely on cloud syncing to update content. If that bridge is closed in a app, the shell is otherwise virtually useless. Standalone apps with offline usecases can often still be of good value.
Youtube apps have become more of a gamble in windows 10 mobile than windows phone 8 in my experience. But if the app is good, i think it is a better investment than using youtube.com in Edge.
UWP apps that support both windows 10 mobile and windows 10 are a good investment, and will still be valuable in the long run, in my experience.
Apps that are supported in iOS and Android is a relieving pitch for future planning, when my windows phone device eventually dies. But I think by that time microsoft will have a new interesting proposition of a device that is the best of pc and smarphone/tablet hybrid, bridging the gap of having to hastle with multiple devices in everyday usecases.