There are certain SRT features that are optional on R/T models:
HID's are standard on SRT (option on J package R/T)
Electronic Convenice Group is standard on SRT (option on J package R/T)
20" wheels are extra cost option on R/T (different style than SRT wheel)
Limited slip differential (aka: anti spin) standard on auto or manual SRT - (only R/T manual gets limited slip)
Unique items to SRT trim:
SRT specific 20" wheels
4 Piston Brembo brake system with slotted rotors
Suspension tuning (stiffer), larger sway bars specific to SRT
Performance gauge package (G-force cornering, braking, 1/4mi, 1/8mi timer)
13-speaker Kicker system option only for SRT
functional hood scoops (cools engine compartment)
leather /alcantara (synthetic suede) seats unique to SRT - plus those versions have larger side bolsters and taller seatbacks.
Interior seems to be upgraded a bit over the RT (more trim)
Exhaust is upgraded as well, including Header style exhaust manifolds
AND...... A Gas Guzzler Tax (Sometimes known as a Fun Tax)
I'am sure I may have left out an item or two.....bottom line is that you are getting an upgraded RT that would cost a lot more if you did all the upgrades on your own................
Is it worth the extra price.....that's for each person to answer on their own. I purchased an SRT8 because in 2008 that was all there was. Had the RT been available I may have opted to go that route and not having drove an SRT I wouldn't know what I was missing...so I would have been very happy. However, having owned the SRT for over two years....I wouldn't be happy with the RT now. Not that the RT is any less an auto....it's just that I have grown to appreciate what the SRT offers.
And, before any RT owners start to throw rocks and bottles....with the SRT comes a few items that might be considered on the "down side"....such as parts cost more, service costs more at your local dealer for some things like Oil Changes, no MSD which means a few MPG less than the RT, no life time warranty available for SRT. BUT, having said that.....there is nothing like being the big dog on the block........