You asked for an economist, so here goes ...
First, there are no guarantees that high quality music will be available anytime soon via the internet. Yes, it will likely be there some day -- at a price. I would guess (hey, that's what economists do you know) that you will be able to pick and choose your favorite songs to download for a price. Of course, formats will need to be determined and playback equipment will need to be designed -- right now, the DVD and CD recorders on the PC are the most likely candidates since they are exist today. All of this may be moot (see Rives comments above) if the legalities and copy protections can't be worked out.
Sometime in the next five to ten years, I would guess that a direct method of recording, editing (tweak the compression, bass ...) and playback will be available for download for something beyond MPx. But, will quality be a top priority? Plus, from what I've heard here on Audiogon, the attainment of high quality takes time (CD's sound much better when they are copied at normal speed -- the bits are all there, but the timing is off when copying is accelerated). So, for quality, you'll have to pay for the music (gotta pay the piper ;-)) and you'll have to spend a lot of time properly downloading it. Since time is money and money is money, the overall expense will go up! Any interference on the phone/cable lines may also add noise; that will not bother most folks, but we are not most folks.
In a nutshell, I'm keeping all my recordings. If for no other reason, I won't have to spend the time rerecording them later. Plus, it will be a long time before the quality we seek is available. Will that change by the end of the decade? Probably. But what doesn't? They still make turnables so they will make CD/SACD players for some time since the stock of recordings is so large. Then, we'll talk about the golden age of digital recordings when the download jitter didn't make the music sound so cold.
Will the recordings be worth more in the future? Some will (recognized high quality and rare). But only so long as there are those who care and demand the old recordings -- that won't last long, maybe another 10-25 years depending on the quality level of the subsitute products (that may be long enough since "in the long run, we are all dead").
The value of your collection is as high as the enjoyment you get from it. Something else will come along that's better (hey, maybe vinyl will see a resurgence) -- that shouldn't diminish your enjoyment overall or today. That is my prediction and is worth every penny you paid for it!
