The SRT area of the forum will have more specifics for the SRT but I can tell you what I know.

First if the crossfire is a true SRT-6 it has a supercharger regardless of year. To be clear though in 2004 there was only one model. It is commonly referred to as a "limited" although that name came around in the 05 model year as there were some changes. In 05 there were 3 models:

The base coupe (stripped down version of the standard 04 model, cloth seats, no fog lights, only black color etc.)
The limited ( basically the same trim as in 04 minus the auto dimming rear mirror)
The SRT-6. This came with the supercharged 3.2l amg engine, larger fixed rear spoiler (aka the whale tail), different wheels, upgraded suspension components and a few other changes inside like different seats)

There were only a hand full of SRTs ever made, if your looking at an 06 SRT it was probably one of the last batch made. I advise looking through the forums and familiarizing yourself with photos of both models. It is veeeerrrryyyy easy to tell the difference once you see both and know what your looking at.

If your browsing ebay and craigslist etc you will most likely run across some limiters or base models sporting SRT or AMG badges, do not be fooled by these. An engine bay picture is worth more than anything in those cases. A supercharger is going to be there on a real SRT.

My crossfire was a daily driver for several years and was used for several road trips as well. It's basically all mercedes components so aside from the few know PITA issues that are documented on this forum these cars should last a long long time.

Hope this helps and welcome to the forum!