I know they're expensive (though a low-end macbook air is pretty reasonably priced) but I've found it well worth the money given it's what I spend almost every waking hour in front of.
And with decent enough hardware Linux runs very nicely under a virtual machine when you need it.
Following this logic, should I have bought a latest Windows PC to run the program or two I run under Wine?
Why would I want to do everything inside of a Linux virtual machine, as opposed to natively?
If it's only for one app, no.
I just personally find the mac platform in general to offer a better user experience, esp. with regards to not having to waste hours getting stuff to work.
This is just my personal experience; if Linux works for you then great.
In my very limited encounters with OS X's desktop environment, I didn't find it practical, and the proposition is: take it or leave it, right? Changes to the default desktop environment are as outlawed as they are in Windows, or aren't they?
I use slate + pckeyboardhack + keyremap4mac to control my windows via keyboard. Instead of using multiple monitors I switched to a single larger one which is easier to control.
I guess my point is that you can kind of change things, but you might need to compromise in some areas. I don't know of a way to get multiple desktops, for example, but I can switch between apps by binding keys to names of them and get around that way.
It's also going to be hard to try these sorts of things out in the store, and given how expensive the devices are it's difficult to justify given you may end up with an expensive tool you don't want to use.
YMMV, of course.