Hi,
I'd recommend the following upgrades:
Replace plastic suspension hanger for aluminium:
http://www.rccarshop.co.uk/index.php...-3-degree.html
Replace plastic rear toe block for aluminium (either one of these)
http://www.rccarshop.co.uk/index.php...ee-dex210.html
http://www.rccarshop.co.uk/index.php...unt-1-5-3.html
In my opinion the plastic parts are liable to breakage and upgrading will strengthen the rear so breakages won't happen.
Apart from that the car is really good as RTR. Changing to mid motor only needs a few bits and costs less than £15.