I do not regret getting my cap at all. I just got back from a vacation to Cape Hatteras, NC. It rained when we got there and we got pummeled on the way home. Without the cap the contents in the bed would have been soaked and not at all safe from sticky fingers and the elements sun and wind.
I keep my Knack gangbox and assorted other stuff in the truck at all times. I rigged up two dome lights in the cap and a constant 12V power supply at the rear. The lights are on 3-way switches. One switch at the rear, (next to the power supply), and the other just inside the sliding front window. Having a sliding rear window on my truck's cab is something I would not want to be without.
I just picked up a 6 X 8' steel bed trailer with removable wooden sides from a bud for $75, (including hitch and ball). After the title transfer and repairs/additions, (another 75-$100), I'm as happy as could be.

I'm curious, what does one haul that the cap would not allow you to? How often does one haul these things? I considered these questions before I bought the cap and dismissed them due to my personal answers.

Do the math and factor in convenience. Remember: Work/live smarter - not harder!

All I have to do now is finnish working on my planes and find the number for Mother Nature so I can request she ease up on the wind and rain.

BTW, since I can be pedantic at times, I checked on the actual price of my used cap. $541.50.