I don't think "VFR not recommended" is a cover-our-butts response of the briefers--it's mandatory for them to say it when the weather is marginal. But it's also worth taking note of the warning, because not all pilots have the experience to put their nose in it safely. Sure, if you're particularly familiar with the area and have many hundreds, maybe thousands, of hours and have done a lot of extra studying of weather phenomena, it's fair to second guess the warning--I've done it many times. The complacent newbie who has maybe 2-300 hours and thinks he knows it all should pay attention to it, because he doesn't. And like so much in aviation, the hard part is knowing that he doesn't know.
I do agree that briefers who are pilots tend to give better briefings, even the L-M FSS briefers. They tend to think like pilots (duh!). The other day, when I called for a quickie briefing for my little flight over Rocky Mountain National Park (I had checked DUAT already, via the AOPA website), the briefer was clearly a pilot. He gave me the usual airmet warnings about cloud obscuration of the peaks, icing in the clouds, and that if the wind picked up, which it was forecast to do come evening, there would be a sigmet for turbulence. When I said that sounded pretty normal and that I'd likely be on the ground back at Greeley by 4, he said, "Looks like a nice flight--wish I could go with you!"
But I've also gotten some pretty awful briefings, especially when the L-M computer sends me to a non-pilot briefer in Raleigh who has never seen the Rockies. It's hard for them to identify with what's going on where the rocks extend to 14,000', when the highest peak on the east coast is only 6700'! I can usually identify the beginning of a bad briefing, when the briefer asks "what state is Greeley in?"

Cary