Mostly I take it that those Registration Cards that come inside the Soundtracks are for general demographic information-gathering about the purchasers, but...

There's been more than a few times I've noticed that they mention Bonus goods, contests, and prizes for mailing them in before a certain date, or for being within the first x number of ones returned...

Other than being disappointed about missing out on cool (and free) goodies, does it seem worthwhile to try and fill in our Foreigner Information on these cards and send them to a friend in Japan so they can drop it off for us anyways?

If they're looking for consumer data, that would at least show them there are foreign consumers, even if the only result is some mild amusement / bewilderment on their part.

They might not even be willing to send promotional items outside their country.

Well yeah, obviously we wouldn't gain anything, I'm just saying it sucks how we can't "fully participate" even after we've made our purchases.

Aren't they more aware of our presence nowadays? I mean like word of mouth to their collegues whenever we amerika-gaijins ask them to autograph some obscure album they worked on 15 years ago? Not to mention the increasing internet buzz/advertising, etc..

I think it's illegal to, actually

I don't think they take them in consideration if they don't feature a Japanese address (jpn postal code) since they're being computer processed. It wouldn't harm of course but it's pretty much pointless.
Later,

Alcahest

That's probably quite accurate, that any additional data which doesn't fit the desired profiles will only be discarded, rather than be something to inquire about. 

Is anyone certain that these are handled by a 3rd party data collection company and not actually submitted to the record label which produced the cd??

The composers are getting more aware, but not the producers and executive producers of record labels who are the decision makers of what cd releases get created.  It's not their fault though, as non-domestic markets simply aren't within the scope of their business model.