First of all I don't think 'investment' is the right word. Whatever you buy will lose value so what you want to do is minimise that loss.

There is probably only one fail-safe answer; Briggs and Riley for their iron-clad, 'whatever happens' warranty. Rimowas are often repairable but their warranty doesn't necessarily cover airline damage. It's just a shame that B&R aren't the most attractive.

I wouldn't worry about spending money on check-in luggage which is more likely to get damaged, that is exactly where you *do* want to spend money.

In your situation I would go for two four-wheel spinners, simply because they are easiest to handle when wheeling them together, and at the same time giving most flexibility.