That's actually a great idea and it never occurred to me. Oddly, I have two sets of the 4 high Sterilite shelves in a 5-3 configuration, and didn't think of applying that customization to the Alera, especially your idea of a rolling work cart.
I just threw the extra shelf collars they give you and the stationary feet in a bag and tied to the shelf like you did; it just looks kind of crummy. It really is a nitpick though; these are great for the money at this price, even with tax. Buy.com have a warehouse right down the road so I received mine in one day.
My dedicated 'work bench' is plastic shelving similar to Sterlite(36x24) set up with three shelves,,,four units wide along the wall. That left me with enough shelves to replace the original shelving in our 44" wide garage cabinet. Gave us ventilated shelving and freed up a few inches of tall space for long-handled items, etc. Felt weird putting pre-fab shelving units INside a cabinet; but DW is very happy and it has worked out well. Beats storing paint cans on MDF shelving with no front support!
By the bye.2...I made sure my strongest wheels are on the rolling cart set-up. It gets moved more frequently than the others, so the wheels see a bit more action. Also, the easier the wheels can turn, the better, Moving the units on carpet or a woodchip laden shop floor is a recipe for wheel disaster. Once the threaded stem of the wheels starts to bend, I don't believe there's any turning back! On that same point, new owners of these type units should make sure the wheel assembly is threaded ALL THE WAY into the post. Otherwise, it is much easier for the threaded stem to start bending. No reason to wrench-tighten the wheels, just make sure they snug up against the bottom of the post.