I worked for said company for 5 years. I have to say I agree with most of whats been said. I usually only go to Halfords now when i know exactly what I want. Tools and consumables is probably their main attraction to me.
What i think we need to remember is that most of us here are enthusiasts to one degree or another. Halfords main aim is really to cater for Joe Bloggs who needs a head lamp replacing on the cold rainy drive home from work, or a roof box supplied and fitted a few hours before the family driving holiday to France.
The generalised nature of a number of their products simply boils down to allowing for greater profit margins. If Halfords were to have a bigger range of products to capture the car enthusiast, it would put them more in the market of the like of Demon Tweeks etc, which frankly they would struggle to compete with in terms of service and product knowledge. That's largely why the Ripspeed brand fell on its arse years ago.
Which brings me to the next point. Staff. Yup, most people on here probably know more about what they're looking for than the staff do. But most customers want a store colleague to simply tell them what bulb/wiper/battery etc they need and offer to fit it, most people aren't too interested in the finer details. There are staff that may be able to offer more insight into what they are selling, but when your simply selling something over the counter and not using it, unless there's a problem you don't know whats good or not.
Regarding the 'WeFit' service, if they break it they'll pay for it to be fixed. But like most i'd rather fit my own parts. Bear in mind the cost of fitting say a brake bulb plus the part would be the equivalent pay for that member of staff for an hour, not just the 10 minutes or so to actually do it.
General rule of thumb, pay peanuts, get monkeys.