When you have a look at MacOS X 10.3, 10.4 and 10.5 you may notice something interesting: Each of them added functionality but ran faster than it´s predecessor. The amount of RAM used was however increasing, but never doubling.
Clearly they were trading time for space, which is quite common, I believe.
So efficiency is a tradeoff in any case. But if an OS runs slower and needs more RAM and only adds features that aren´t noticed by the casual user ...
... I could´t justify recommending that, even if it was "modern" and "compatible".
I don´t mind eye-candy though. Most of the time it comes pretty cheap. Beautiful pixels take as much RAM as ugly ones.
