Sales pitch? No one on this forum is trying to sell you anything, and to my knowledege there are very few actual merchant reps on this site.
What we are trying to do is help you out. If you are upgrading to an OS, Fantom or just about any engine out there from a TRX Pro .15, CVDs are a good idea. You do not need to be a competitive RC modeler to need them. With a properly tuned TRX Pro .15 I was over torquing the stock slider axles. I then dropped a Fantom in my Maxx and that was all she wrote. I went out and bought the CVDs within a week.
All I do is bash. And one thing I know to be fact is that constantly repairing your RC gets to be expensive (even if all you are doing is making multiple repairs to the same cheap plastic part).
Now on to other hop ups. Metal has its place in certain areas. I would not waste the money on A-Arms or skid plates unless you intend to go straight to titanium (a very expensive move). Aluminum bends easily under heavy impacts (the kind you might experience in bashing backyard or otherwise), and when it comes to skid plates reshaping them often requires removing them from your RC (a real pain in the...). If you want to get something that it just about bulletproof, I'll recommend anything RPM makes. Why? Because if you break it, they replace it no questions asked.
Things that are good to make metal: Bulkheads, shock towers, chassis braces, bulkhead braces, center skid plate (this is the only one I recommend), steering servo skid plate, tuned pipe, and shocks. If you really want metal a-arms, I recommend only doing the uppers. The lowers are the ones that will get the most contact with ground objects making them more prone to damage.
I could go on and on about the goods, bads and others when it comes to hop-ups. The bottom line is all going to depend on how deep your pockets are. If they are not deep, then RPM products are the way to go. Great quality, near impossible to break, and if you do break it they replace it.
I caution you on one thing...your RC will break, you will have to replace things...the best thing to do is lay out as much as you can afford to get quality upgrades in key areas that will protect and minimize breakage during those "bash" sessions.
One final note...UE SuperMaxx hop-ups and pieces are some of the best out there. The pricetag reflects that quality, but in most cases...it is overkill for the average basher, and not worth the price.