I have loads of equipment with Kadee #5s, but I only buy #58s since they were introduced. The difference in appearance is dramatic enough to me that I'm slowly purging myself of the #5s. Any plastic couplers, including the plastic Kadees (not sure of the number) that come with Eel River Models beer cars, are removed as soon as I have a package of #58s on hand.
As an aside, I also have begun equipping everything with semi-scale wheelsets. I'm not crazy or patient enough to go with full Proto 87 wheels and Sargent couplers, but I am conscious of the appearance of both wheels and couplers.
I have a few unit trains (grain and coal) that I've equipped with #58s and Walthers dummy couplers at a 1:2 ratio. In other words, in a six car cut where "A" is a car equipped with Kadee #58s on each end and "B" is a car with dummy couplers on each end, the cut is assembled like this:
A B B B B A
It eases the pain of buying dozens of packages of #58s and the two couple well (not automatically, of course) once you've removed all the flash from the Walthers coupler. Kadee #5s don't fit quite as well with the dummy couplers, so they've been removed from the unit trains. The dummy couplers look great, they couple tightly which reduces slack significantly, and they're really inexpensive.
As far as using different length shank couplers is concerned, I snip the glad hand off every coupler right away, so I don't have to deal with any coupler other than the #58 on locomotives.