Like above mentioned, ONLY depends on WHERE you want to be alum or Titanium......
Knuckles OR C-hub, pick one, NEVER both, if I have to choose, I will pick knuckles, cause C-hub comes with different degrees, from 0 to 6 degree, in order for you to collect them all in aluminum, it will cost you WAY more then $100 just for alum C-hub...knuckles are always knuckles, only left and right.
The reason you only need to pick one....when in IMPACT, SOMETHING must go...there are NO SUCH THING is bullet proof, not in RC, not in real 1:1 car, simple math and phy. period, something HAS to take the impact and BREAK From wheel, to knuckles, to C-hub, to pins, to arms, to Toe-blocks, to pin again, then to the CARBON FIBER chassis.....if you have to ask me, I will definitely let the ARMS (front or rear) break....that is the cheapest part for the whole suspension structure (yes, C-hub and knuckles are using less material but they are more expensive....). When you ALUMINUM the whole suspension.............everything is as strong is it is....except, the weakest parts might be your $65 carbon fiber chassis.....the last thing you want to replace is your CHASSIS.
The worst thing for you to do is UPGRADE everything to aluminum....yes, they might LOOK strong, but they are NOT as good as you think they are...they won't break, but they will BENT........now, you have a bent arm, bent C-hub and bent steering knuckles (that you might not even know), and they are not BROKEN, but bent, totally OFF from your setting, you will have a hard time to find out why your car drive like Sh_t, but you know for sure they costed you $100+ for them, now what are you going to do...? Throw them away or let it be OFF forever....?
When I was young and knew nothing about RC...I used to be alum this and alum that RC Bling Bling racer....now....I just let it BREAK and replace them with their original parts, but then, I learned a real BULLET PROOF way after 20 years of racing - don't crash and don't touch anyone and any wall.....that is the real BULLET PROOF way (but I am still trying to do that...LOL)