The only upgrade needed is replacing the stock drive shafts with Traxxas Stampede or MIP if you don't mind the cost. The Traxxas uses the same yokes as the Axial so it's less than $10 and solves the driveshaft breaking/twisting problem. If yours is an RTR you may wish to replace the lower links with stronger ones either store bought or homemade. The gear cover is a nice item.

The stock shocks work well but have very little bling value.

OTC steering looks cool but messes up the handling.

Buy what you need to complete your scale build, it will never be a comp crawler so don't waste money trying to make it one. It rock crawls pretty good for a scaler.