I'd keep it, all things being equal. The resale value would be quite small, from what I've seen. And it can't hurt to be conversant on as many platforms as possible. The Mac may not have a big slice of the overall pie -- but in audio, it's still a significant presence. (And, of course, in prepress graphics, it's the de facto standard.)
The eMac actually has the best performing HD system of any but the top of the current Mac lineup (at least as of a few months ago). It outperforms all but high end PowerMacs with RAID setups, as I recall. (You can compare various aspects of Mac model performance here:
http://www.macintouch.com/perfpack/comparison.html
With regard to "easy to learn"... yuh, I dunno. I'd read fairly extensively about OS X and its GUI, had a number of walkthroughs with friends, and sat over the shoulder of a number of Mac users -- but when a G4 Powerbook dropped in my lap for a couple weeks, I was flummoxed by how much OS X looks like XP but acts so differently.
Most of that was just things like button placement and 'inverted' functionalities (click on the top bar of a window in Windows and it pops up to maximize or down to float -- do it in the Mac with an open window and the window disappears...) And, don't get me wrong, I don't think there's anything inherently better or worse in the way either of the platforms does things -- but they are different in quirky little ways that can throw you at first.
I was (secretly) almost a little afraid that I'd "fall in love with" the OS X GUI.
Not to worry... even though I'd built up this idea that the Mac had a much more logical and straightforward system access structure -- I found that the reality was often quite hard to intuit. I had to call my Mac pals more than a few times just to sort out what seemed like the simplest of issues. These are things that you get past, of course. But I was surprised, nonetheless.
All that said, I've lately found myself showing my clients how to do some things on their Macs that they didn't know how to do.
One client had a bunch of Photoshop PSP files that needed to be saved down to JPGs. I asked him about batch processing and he didn't know what I was talking about. So I called up his graphic artist, a guy whose been using a Mac for about 10 years to ask him. He said, funny enough, he'd just called
his Mac guru to ask him how to do it and
he said it was "too hard" and "not worth the effort."
Since we had something like 90 files to convert there was no way I was going to go with that...
It took me a while to figure out the fuddle-brained Adobe nomenclature (those people really
are idiots) but once I figured out their somewhat odd terminology [someone buy those dorks a dictionary!] it really wasn't hard at all to "record" the process and plug it into their batch processor.
Cracked me the hell up.
Someone should have asked that "guru" to hand convert all the files. Hopefully he'll do some time in computer purgatory doing just that... heh