I'm normally cool with the idea of unopened collectibles for print products, but I'm not convinced that keeping miniatures in the original packaging is good preservation. There are "lead rot" issues to worry about.
There's a
reasonably academic article on the subject on the U.S. Navy's website (because, apparently, they collect miniatures, too!), but I'll give the short summary:
Lead with impurities can corrode if exposed to acidic fumes. A lot of wood, paper, and plastic products release acidic fumes. If those fumes are allowed to build up in an area without a lot of air circulation, they initiate an almost unstoppable chain reaction of disintegrating lead.
Miniatures in shrinkwrap (or a blister) are in a paper/plastic-filled environment with low air circulation. This can be bad.
Here's a true and embarassing story: I buy a bunch of boxes of
Star Frontiers minis from a discounter at Gen Con 1993. I open up some to look at, but leave the rest in shrink. Then I move across the country and leave the whole set in storage at my parents house... until 2004. The boxes I had opened were fine. When I opened the still-shrinked boxes, they were all rotted.
TSR's miniatures are notorious in the minatures community for lead rot. That's because they used cheap lead, cheap cardboard, and cheap plastic foam, plus they didn't sell well, so a lot of them have stayed in the package too long. If I buy shrinkwrapped TSR minis, I now
assume that some will be rotted, and price accordingly. (The last 5 boxes of SF minis I bought were about 30% gone.)
Frankly, buying a "mint in package" box of TSR miniatures is like trying to buy Schroedinger's Cat. You may just own a box of lead carbonite dust. Your mileage will vary with other companies: I've seen a lot of issues with 1980s RAFM, myself.
Blisterpacked minis can rot, too, but at least they can be monitored. If you're collecting blistered minis, make sure you check them on a regular basis. I've noticed a certain "fogginess" on the blisterpacks of corroded miniatures (especially where the lead touches the plastic), so that may be a first sign to look out for (of course, some plastic just gets foggy as it ages, so it's an imperfect warning system). If a miniature starts to rot, you might as well open the package and try to save it (or at least, save the other miniatures it's packed with), because the corrosion won't stop on its own.
Edit:
Some pictures of rotted TSR minis, courtesy of The Miniatures Page. I should add that the degree of "rottiness" seems to vary by product. In the case of
Star Frontiers, TSR seems to have used better lead for spaceships than for characters, so ships are less likely to be found rotted. I believe the spaceships were some of the last SF minis produced, so it may simply be that they got better lead suppliers late in the line.
