I get all my mince from a local butcher, and it's far juicier/superior than anything in a supermarket. I sear both sides on a very high heat, then cook to medium well, add my toppings, and enjoy. My butcher has eaten at Five Guys at the Trafford Center, and he likes it. I haven't been, but some day....if I can get DH to venture out (he hates leaving home for anything).
I've had 2 burgers at restaurants, and found both to be pretty tasteless. Part of the problem is that restaurants in the UK are required to cook burgers well done....and many assume that means so well done that any semblance of flavor is long since gone.
The other issue I see is using pre-made burgers that are pressed/compacted within an inch of its life. Then they go in the pan, and the 'chef' proceeds to mash whatever juice might be left right out of them. The result is inevitably a crap tasteless burger, no matter where you get it....I've seen the same thing happen in the US.
Can't help with the velvetta, but I 2nd the comment of mixing jalapenos with tomatoes to make your own 'rotel'.