i a, assuming you've researched into aluminum, and you are sure that is what you want but it can be quite expensive, for example: the only aluminum part ive ever bought is an associated front bulkhead. plastic would've costed me £1.99, I ended up spending £12.99 which would be about $17.50. see my point?
anyway, if you are sure that is what you want I'd choose the parts which you find easiest to break, because there is no point in spending a lot of money on aluminum parts that you wont break if they weren't aluminum, so if your budget is small, get the breakable parts, the more money you have, the more you can spend. I currently have a couple of aluminum parts on my b4 (none on my others) no complaints really, they protect well but damn expensive.
but of course the e-revo isn't really a buggy so i wouldn't recommend aluminum, much like miller time said rpm arms are better apart from if for looks.