I think it's very hard to predict what'll happen in the future in regards to value as this is kind of the 'first generation' of electronics that have massive pop culture identification and appreciation. I think the closest thing to boomboxes that goes back further would be the space-age tv's from the 50s. Things that are a design icon will always have appreciation far beyond the generation that grew up with them.
About 7 years ago I was helping a woman try and sell her doll collection through eBay. She had a huge collection of highly valued dolls she'd collected her whole life. Lots of rare dolls worth (apparently) four figures, very few even left in existence. The issue we found is very similar to Chris's Victrola example. She had no market to sell to. Most doll collectors were retired women, now getting into their 70s and guess what? The younger generation didn't give a ****. We're (still) going through a huge low ebb of antique doll values and unless a new generation comes along and gets interested in them they'll be lost to history. There has to be a new generation coming up that cares about something for it to retain/grow in value.
I think that's where boomboxes differ as there's a huge appreciation for them in generations down to teenagers and from many different cultural backgrounds. That alone is what leads me to believe they'll live on and grow in value. I think the toy side of collectables with value has seen its last generation as toys are no longer of interest to kids and it's all technology they're interested in. In 50 years time there's a very good chance that toys in general will drop massively due to today's children having zero nostalgic affinity with them. OR it could go the exact opposite and they discover toys as adults.
I find it very interesting as to what people will want in their lives, from the past, and be prepared to pay a premium for. I'm pretty convinced though that iconic boomboxes won't drop in value in my life time. There's just too much cross cultural attachment to them, but really, I'm never going to sell my collection and certainly never ever bought a boombox (or toy for that matter) for investment value, however I did have something interesting happen last year that gave me some faith that my collecting instincts are still nicely honed.
For those unaware I collect a tonne of different 80s stuff, way too much to go into here, but last year I had a self made millionaire dealer who's business is knowing what to import/get made from overseas market to sell to collectors and those interest in niche items visit me. He came into my house and was amazed and looking at my boomboxes and other items, he said 'You're so far ahead of the curve, give it a few years this is going to be worth a hell of a lot of money'.
Everything is cyclical, add 20-30 years to anything and it becomes valued again, just look at records. The real magic is keeping something valuable beyond a passing fad or phase. Then again, all it takes is one movie or TV show to re-iconise something and BANG! it's off again!
My moral for my entire collecting though is buy it to love it, not profit off it. If you collect that way you can't lose.
Rock On.