The differences:
-Shocks towers/front and back
-The Shocks...the roller has aluminum top and bottom caps
-I believe the chassis on the roller is the hard annodized chassis...thicker aluminum so it will survive the numerous triples/doubles/a brushless chaos that you can throw at it...
Thats about it....and you can definitly recoup the costs after selling the spektrum radio and all the nitro stuff.....nowadays on ebay the radio/rx can go for $100.00....and the unused engine can sell for around $80-$100.....and the unused nitro stuff can go for about $20-$30..........so max you are looking at is $230....

....now for brushless:
Mike's motor mount=$50
Mikes battery tray=$40
so that's $130 leftover for a motor/batteries....