Personally, I'd stick with plastic for arms and towers.
I can beat the living crap out of mine and it rarely goes down due to injury.
Non-stock:
RPM arms
Lunsford turnbuckles in RPM arms
Lunsford turnbuckles for steering and rear (not needed on rear for LST2)
RC Raven dual rate springs with 45-60 weight oil (I run 60 weight)
Dynamite engine brace
Hardcore Racing titanium chassis (got lucky on buying that!)
HD Diff cups with 50K OFNA oil
HD center skid (the one that protects the pipe and spurs)
3 shoe HPI teflon clutch shoes
4mm bolts for towers to bulkheads
4mm bolts for shocks to towers
4mm bolts for engine mount underside
3mm bolts for everything else
Then there's my "homemade" upgrades:
Roll bar that makes contact with the body, dual purpose, protect the engine and possibly shocks (with the design I went with) and since the body rests on it, it helps avoid buckling/cracking when you do end up on your lid.
front-to center aluminum skid (key upgrade to avoid replacing damn chassis rails)
rubber bumper supports
I also run smaller than stock tires for less rotational mass and leverage in cartwheel type landings. I'm currently running revo 17mm rims/tires.
To be honest, the homemade upgrades were probably the cheapest and best durability related improvements. Since the front-center skid plate install, I have not busted a single chassis rail. Been 2 years and many gallons of abuse. Prior to that, I had 6 months and 4 or 5 sets snapped. I did get the HCR chassis at the same time though... so between the two, the core of my truck is like a tank.
EDIT:
Tried to find my "skid plate" thread, but can't, so here's a few shots of my aftershock mess:
Skid plate:
Roll bar:
Roll bar mounting (HCR chassis was done later than these photos):
rear-
Front:
Bumper support (similar on the rear):
On the shelf... waiting for summer:
My LST2 has the alloy frame rails, hd full alloy skid plates and steering. and the list goes on. I don't break it hardly ever anymore. just make sure that when you do reinforce that you are fixing the actual problem, you can be troubleshooting why the drive cups aren't fitting on the LST series and it will be because you bent a top chassis support or an engine brace. One more thing when you are upgrading, I tried to stay with the stock arms that way when I went WO into something and tore the arms off it was cheap to fix and the important things stayed safe. seemed to be a fairly cheap failure point.
