I would say ask yourself "what is it that I want my truck to be able to do, but it can't" and go from there.
If you just have money burning a hole in your pocket, I'd save it for gas for a trip somewhere.
What do LED's do for you? Is the regular light insufficient for you?
As far as a shell or topper, my advice would be to buy a used on off of CL, but then I'm a cheap bastard!
A new fiberglass shell will run you $1000 - $2000. I've put 3 shells on 2 different trucks over the past 7 years and my total cost (for all 3) was $650. Two of them, amazingly, were even color matched to the truck I put them on.
Personally I don't care for canvas toppers. My thought is that a canvas has most of the disadvantages of a metal or fiberglass topper, is more difficult to install and remove, and you can't lock it. If you don't need a real topper, then an open bed is more useful than a canvas topper. You can even bolt a waterproof, locking tool box into the bed of your truck if you need to keep stuff secure or out of the weather but you still want full access to an open bed.