I agree that the law of diminishing returns definately applies, but that is not necessarily a bad thing. There is excellent equipment that costs $2000 a unit, and excellent equipment that costs $5000 a unit. The difference here is not usually going to be as drastic as comparing a $200 unit to a $1000 unit, but the difference is still there. In my opinion, if you aren't sure what those differences are and whether or not they are really worth it, than you are not ready for the higher priced unit, go with the less expensive one. A lot of the differences between the higher end units is definately subjective, but that does not mean that they should not be valued as they are. When you are ready to fully take advantage of those differences, you will know it and the price tag difference will not seem like such an issue.
In general, I do not think you are going to have much luck buying a unit for half what another costs and still get the same quality. Today you may not notice the difference much, but down the road as you get more experience, knowledge, time, and develop your ears more those small differences may become more and more apparent to you as well as more and more valued to you. In this day and age however, there seem to be more "bargains" popping up. Those to me are the items that you buy that outperform their price point. It does not necessarily make them as good, but there is definately a more solid "middle ground" now than there was 10 years ago.