I think the PRICES will continue to go up. Just like everything today - pizza, coffee, wheelbarrows, housing. Inflation is in double-digits and EVERYTHING costs more.
As for VALUE? Like any 'collectible' item, I think as time goes by, it will also continue to go up. Not only for nostalgia's sake, but because of attrition. No matter how much we love these cars as a whole, and take good care of them...every day/week/month, some of them are destroyed. Parted out, accidents, whatever. And, they aren't making any more.
Overall, I think they'll still increase...but modestly. For that to happen, the price needs to rise at a slightly faster rate than the inflation rate. But the G2 Charger has established itself as an 'icon', and enough people love them for their own reasons...I don't see it declining anytime soon.
Would I buy one (or ANY car) as an "investment"? Never. If you want to use it as "a car", the risks are simply too great - traffic, accidents, dings, bird droppings, dust, dirt, stone chips, cracked glass. And I have neither the means nor the desire, to do that to an amazing automobile (or motorcycle). They deserve to be used as they were designed - driven, enjoyed, seen, touched, heard...kept moving, not just sitting somewhere. And, when it comes down to it....they're toys. We don't "need" them. Their value, and their price, are completely up to the whims of peoples emotions.
I own a '70 Charger 500 because of family history (mom bought one brand new and I never got the opportunity to enjoy it because my cousin totaled it in the mid-70s), and personal desire. I love it, warts (unrestored) and all. I love driving it - and, being unrestored allows me to drive it guilt-free and relatively worry-free, compared to if it was a perfect, concours-restored car. If my family wants to sell it after I'm gone, and it makes some money for them? Good for them. For me, though - it's about the car, and the experience, and the fun...not the money.