I personally disagree with about half of it, though I did find it to be well written and I think you did a good job on it.
I do agree with you on the broad point that there is a need for some type of change to the current system, though not to the extent I think your advocating. I totally agree that it is absurd for a man dead to still hold rights (financial) over an idea, and others still need to pay royalties and what not to some heir or trust, whatever it may be. A dead man has no rights, though I'm sure that will invoke a response from some, spouting some meta-philisophical non-sense, it is very true.
My belief is that man does have sole ownership of an idea, more so than anything else in this world. I believe that if his ideas can be used to make money, he is entitled to reap some type of benefit from it, and rightfully should, so long as he draws breath, but no longer. Others can be free to build upon the man's idea, and reap the benefits from it, and so on and so forth.
You seemed to really cast aside the argument of dampering progress, basically saying it is a non-point, as if only the greedy would care so much about wanting to benefit from their own original idea. What other motivation do they have? You can say that they should want to "for the greater good" and "for the betterment of society". These are both great Socialist ideas, that leave the opposition no room to argue, save they sound like a selfish bastard, which is why they are spouted out so often as some end-all argument. I would argue that the best thing a man can do for society would be to be as selfish as possible, so long as it does not take wrongfully from another.
For example, lets say I work to figure out a better way to transport bananas from South America to the United States that will allow them to stay on the shelves a little longer. I come up with some great method of harvesting them that will do just this. Why? For the good of society? No, I did it for personal pride, reward, and to help put food on the table for my 19 kids. Who benefits from my idea. Just me? No, everybody does. Every grocery store in the country and can now save money, since they are not throwing away so many bananas. Hey, look at that! Cost just went down on bananas. Who profits? Society does. The man who came up with the idea didn't do it because he wants to spend a little less on bananas. That was not the force that drove him to come up with this idea. He did it for himself and his loved ones. Does him wanting to be rewarded make him greedy? If he wasn't, or if he knew going in that he would not be, do you think he would have done it in the first place? Maybe he would have, and maybe he wouldn't have, but what would you put bet your money on would be more of a drive?
I know I kinda went off on a tangent a little bit, but in summary I think that ideas should be protected and the creator of the idea should be entitled to benefit from it, though only for the span of his lifetime. You may try to argue that society should have ownership of an idea, but if that is the case, you will soon find that society runs out of ideas.