I am not a neuroscientist, but given what we know about artificial neural networks, it seems to me that forgetting has to be a necessary part of the learning process - allowing neural pathways to be reconfigured to whatever you are learning.
We know with artificial neural networks, that training towards one goal necessarily comes at the expense of other goals - and for a given network, the more different patterns it has to be able to recognize, the harder the training is and the more error prone the recognition is. Now of course the human brain is way more sophisticated than even the most complex neural networks we have devised to date, but I think the principal is the same. We start out in life with billions more synaptic connections than we have as an adult, with the number rapidly diminishing as we learn how to walk, communicate and function in society - which makes it possible for us to learn just about anything as a child, but also as we get older makes it harder for example, to pick up languages or even change our accent.
Although it is possible to learn an instrument, be good at martial arts, be able to paint a picture lworthy of hanging in a gallery, write a sonnet and remember all the details of what you had for breakfast 10 years ago, the more you try and improve one area, the more the other areas will be slightly degraded, as the synapses are rearranged to do whatever it is you are learning.
With enough practice you might be able to excel at several of these things, but something has to give. I wouldn't be surprised of the myth of the absent minded professor has some roots in this - the more specialised and in depth your learning and knowledge is on a subject, the more unrelated and unused areas will suffer.
Of course, someone with an overall larger neurological capacity might be able to learn more of these things, but specialising in one thing will I think come at the expense of being a generalist.
Thats why we need experts in different fields - because you literally can't learn everything and be as good at all things compared to beign very good in a particular field.
Personally speaking, I know I am awful at memorising things, but do very well at figuring out problems - I am sure if I somehow becamse a lot better at memorising things, my problem solving skills would diminish.
Now some people have started messing around with "smart drugs" that can accelerate learning, I'd lay money on it that it will turn out that they do indeed help you learn whatever it is you are doing faster, but at the cost of greater degradation of past skills and memories. I wouldn't touch those with a barge pole.