All Avalon miners really are is extensions of your computer. Instead of using USB you connect to it through ethernet.
Honestly, I wouldn't want, nor buy, a miner that requires my computer to be on or connects to a motherboard directly and requires a PC motherboard to function. I'd rather have a specialized box far away in some basement than inside my computer. It just creates more hassle than is necessary.
I can see 'casual' miners as PCIe extensions such as 'casual' miners in USB thumb drive format.
Though honestly, anyone buying a USB thumb drive is doing it more for the novelty than mining. Same would apply for PCIe cards.
I disagree on the PCIe front. Many miners currently have GPU mining rigs, so if someone could manage to get 10-20 GHs out of an ASICs PCIe mining card, and can run up to six of them per computer, you're talking about some decent hashing power.
The question is relevant as miners sell off their GPU mining rigs. It might be a no brainer to sell the GPUs, but what about the motherboard, CPU, RAM, drives, and power supply? These items typically have a lower resale value than GPUs, so it may make more sense to hold onto them if there is potential re-use value in the future.