I updated my original post, I had to go take some better pictures of my One18th stable.
I haven't really replaced many parts with aluminum on my Mini-T except the steering knuckles because they stripped out when I wrecked it. The chassis set is only $6.00 at my local hobby shops, and almost any stock replacement parts set will be under $10.00 which is a plus for the stock parts if you bash a lot.
The parts I highly recommend are titanium turnbuckles, I have them all around on my Mini-T bug and they do not bend or break. In fact, I was running a set of stock turnbuckles on the front and when I crashed it at almost 30mph into a curb they bent bad. The titanium turnbuckles on the rear of the front held strong. They are very affordable considering the price of stock replacements.
I also recommend a bearing kit, even on a stock Mini-T you will notice a difference. Another good thing is the 7.2v Packs, there are many out there so make your decision on which you want. I went with the Team Losi packs, they perform very well.
RPM Front bumper is a must, I have one on my RC18b and my Mini-T as well. They will save you in low speed bumps, and protect the body quite well. You will notice that my high speed crash did not even effect the bumper and the body was not even scratched.
Dual disc slipper and Ball differential are also great add-ons, as well as MIP CVD's. I have two sets but have not installed them, but anyone will tell you they are excellent hopups.
I don't even want to begin to count how much money is invested in these minis, but they are very fun to drive.