Luggage rack - upper fastener broken. Can it be repaired?
Its steel, so any competent welder should be able to weld them back together.

Your other option is plumbing mounts, something like this.



Imagine a pair of these on each side, with a nut/bolt through that top hole.

http://www.ezystrut.com.au/products/pipe-support-systems/pipe-clamps/e8y/e8y/

Or something like this but with a quarter-turn twist between the two holes.



Another simple fix would be a single jubilee clip around each crossing, at 45 degrees. It will distort on tightening but will hold well enough. AKA a hose clamp.