First: Welcome.

Second: A couple thoughts:

If you are planning on using the business case and the spinner together you are giving yourself the hassle and weight of two sets of wheels.

I can't speak to this specific luggage, but:

1) All luggage scratches and wears. Much less if you carry on and are careful with it, more so if you check it. But it happens.
2) How much you use a warranty depends, in addition to the bag itself: How often you use it (or how long until you'll replace it for other reasons), how often you check it or do other harsh things with it, and how diligent you are about actually claiming the warranty. If you plan on checking it often, then a warranty that covers that damage is probably valuable. If you will carry it on exclusively and will want a new bag every so often anyway, it's probably less valuable. Spinner wheels in particular tend to not be that durable as checked luggage. Note that the warranty on those bags doesn't cover wear, tear, airline abuse, etc...
3) Repair costs depend on labor costs and parts. I think the labor on almost any repair would be less than $50. Parts tend not to break the bank, but that sometimes depends on the brand.

Are you looking for recommendations for other bags you might be interested in? Or just feedback on those specifically?