On the contrary, there are several valid comparisons you can draw:
1. The Superbird was a fairly expensive niche vehicle at the time, like the SRT6.
2. They didn't sell very well either. There were many new untitled Superbirds on dealer lots well into '71, and even '72. By the gas crunch days... You couldn't give one away. (they took a huge depriciation, just like the SRT6)

Collectability is such a fickle thing. 86-87 Grand Natoinals were socked away in garages by the thousands. As a result there are tons of nice ones out there, and they aren't skyrocketing in value.

Generally the cars that end up collectible were either ones that people had or wanted as a youngster, or ones that have aged well and/or represent an automotive milestone.

The SRT6 is/was a beautiful design that is often confused for a current 2011 model today. I think it's lines will age very well compared to other cars of it's era. It has high performance, (almost a nesessity for collectibility) and was built in very low numbers. (and the way insurance companies write these cars off, they are becoming more scarce nearly every day.)
I think it has a far better shot at being desirable/collectible in 30 years than most of the cars of it's era.

That being said, I would not ferret it away as an investment. Drive it, love it, keep it.
It might just be worth a fortune one day. You never know!