Speed advantages are in the drivers thumbs....which is why I'm not good!
Seriously though, you could have the fastest LiPo'd, brushless'd car on the track. If you can't drive then its no advantage. The fast guys will still be the fast guys. They're like that for a reason.
I could put a 5000 lipo and a 2.5 brushless in my car, and I'd still get beat by Cragg running Nihm and a stock motor!
Yes cost is a factor for most (including myself), but I always have to sell older stuff before I buy newer stuff. That way, you don't have to put as many pennies towards your new products.
Club racers will always buy your old gear, and some will even pay near the retail value for it if its in good condition.
Regarding 'modification' to chassis. That would need to be clarified. Would removing the battery trays from a D4 be classed as 'modifying the chassis'?