A lot of this isn't true.
Firstly, mileage on an SRT-8 and an R/T is not comparable. The R/T has a 4 cylinder mode, which is FREQUENTLY in use cruising on the freeway, the SRT engine doesn't have it at all. I know of both a charger R/T and magnum R/T owner who gets 20-22 mpg regularly, with a majority of highway driving. Not to mention the R/T engine runs on mid-grade, and the SRT requires premium. As far as mods being pricey, this was the case early on in the platform, when only a few companies were producing parts, and had a sort of monopoly on the market.
Yes, the charger will feel large, because it is. However, if you're sure to get an R/T w/ the road and track package ( different steering box, exhaust tuning, intake box tuning, suspension, brakes, wheels) , much of the steering/handling of the car will be changed for the better. There is a very noticeable difference between non-road and track packaged R/T's and those w/ it......also, if you get it, it comes with waaaaaaaaaaay nicer seats too.