You can never have enough bikes. Different bikes do different things.

For the clunking, take it to your LBS and make sure it's in working order. If you decide to sell it, best to know now if something is wrong.

If you've had numerous fittings (same LBS or different ones?) maybe something is up. I had several fittings with my Madone. In the end I realized I hadn't truly bonded with the bike. I was sad when I sold it to pay a bill, but I don't regret selling it. It just never felt right and I couldn't put it into words.

How long have you had the bike?

Is there another bike that has caught your eye? Sometimes I think as we get better or more experienced, our needs/fits change. Maybe you've just outgrown this bike and it's time to move on.

I wouldn't sell the bike unless you find something else you are sure you want. Buyers remorse sucks. Then use the money from the bike to purchase the new one.

If anything, if your Crux goes into the shop, you do have a back up bike.