The important parts to upgrade from the very original to the V2 for bashing would be to get the 4 extra tough arms. They were optional on the original, and the .2 came with them, making the lighter weight original arms the option instead.

The rear transmission housing I would consider an option. It straightens the driveline for less wear in the back, and gives the larger bearing, but I've never had problems with the originals and I raced them for years multiple times a week. Having a spare on hand is not bad, especially if you do a lot of wing first landings (this is one type of crash I very rarely do...though I certainly crash plenty in other ways).

In all cases, get an aluminum servo horn if your servo doesn't come with one.

Lastly, since you mentioned an SCT410 for your kid, if you're just bashing all the time, consider grabbing the M2C 17mm hex conversion for the SCT410, allowing you to run normal eBuggy tires so you can share. They're slightly larger in diameter so you may need to mount a body higher, but the M2C keeps the same offset so you should be ok otherwise. Don't use the Tekno ones for the SC, they make it wider like a buggy and then bodies won't fit as the wheels will stick out the sides.