Windpants as useful as Wshirt?

Jhaura,
I often layer my Montbell UL windpants over a lightweight Smartwool baselayer when hiking in conditions I know will be cool and windy (think above treeline hiking in northern Scandinavia in September – temperatures in the 20's (Fahrenheit) to 40s. I find this combination to be more comfortable than wearing more traditional hiking pants (although I suspect that I'm in a small minority here). Coincidentally, the aforementioned conditions are ones in which I also utilize a windshirt. I suspect that windpants aren't more widely used simply because most people can tolerate these conditions without them or simply don't hike in such conditions often enough to warrant the additional expense (and ounces) of windpants (as you suggest).

I have a pair of homemade wind pants from 1.1oz ripstop. Like an ultralight windshirt, I find that they are much warmer than their weight would indicate. I use them instead of light long john bottoms because I can put them on and off without removing my shoes (or my shorts). They go on when I stop for a break or in camp in cold or windy weather, then come off when I start hiking again. In very cold weather they layer nicely over light long johns or Powerstretch tights, and add significant warmth when needed. I find this combination more versatile than high-loft pants by themselves.

At less than 3oz for the pair, including a sewn-in stuff sack/pocket, they are always in my pack.

No, they are not. Under most hiking circumstances, your legs will stay warm enough just from the walking you do, but your body core will need help.

If you normally hike in shorts, wind pants can add significant warmth to your legs if the need arises. Avoid adding too much; it's better to have cooler legs and thereby sweat less under your pack, which keeps your core layer(s) drier, especially if it's a cold windy day.

Personally, I wear long nylon hiking pants every day on the trail. If it gets really cold, I'll layer my Patagonia silkweight long john bottoms under them. For those rare occasions when it's both cold AND rainy, I'll replace the hiking pants with my Golite Reed WP/B pants which serve double duty as both wind AND rain pants. It's never happened, but if it turned unGodly cold – and I have a sane reason to be walking through that crap instead of under my shelter in my sleeping bag – I might wear all three layers.

Wandering Bob

Jhaura, no they are not.
IMO if you can only buy one pair, get a pair of goretex pants.(or if on a budget, Red Ledge Thunderlight pants for $30) They can work as wind-pants, rain wear, and they trap air as an insulation layer over your hiking pants.
In winter I do carry Montbell thermawrap 3/4 zip pants for sitting around camp in the snow, but I assume you are talking 3 season use..

I love my Golite wind pants…I wear them when I am hiking in kind of cold conditions…I wear them in lieu of nylon pants to hike in for various reasons the main one being that I hike in running shorts with the liner (incase you are wondering, I can't find a decent pair of comfortable underwear for hiking so the shorts double as underwear…I know TMI). When I wish I had a thin layer on my legs, these are perfect. They are warm enough that I can keep my legs warm but I find that they breathe enough that I wear them even when hiking out of (yep…up) the Grand Canyon in 60* temps. I think (although I am not sure yet) that they will also help prevent my legs from getting chewed up by mosquitoes when it the temps are up to 70* or so…I won't know for a while about that so I can't promise that I'll be able to remember to report back on that hypothesis. Enjoy,
NITRO
p.s. on a side note, I took a nasty spill while wearing them and they held up great and I fell and slid a bit on a rock (and then hit my head on it and bent my pole)…but my butt didn't get scraped up thanks to the pants…very bruised though.