You should have rain gear of some kind. To do otherwise is risky and at the least, miserable. "Walking through it" seems noble and adventurous, but not so much in reality and dieing from hypothermia would really suck!
I don't think much of using my poncho for a ground sheet, as it will get trashed by rocks, dirt, sticks and roots. To me, the whole idea of a groundsheet is to have a cheap replaceable sacraficial surface to take the abuse instead if my sleeping gear. My groundsheet gets UGLY! I use Tyvek or polycryo.
That said, a Golite poncho is just 7oz and costs far less than anything made in Cuben. It has the right features to be used with a backpack and give good coverage. A poncho makes a great CYA shelter and rain gear option for day hikes too.
I like the Frogg Toggs pants idea. Other than that, one of the light 2.5 layer rain pants will work--- at greater weight and cost, but with better fit and durability.
I think the only way wind pants pay off is when they are combined with super light running style shorts. Otherwise, you might as well wear zip-off convertibles. If the weather is getting cold and windty enough for wind pants, then rain pants will do. Wind pants are fragile and are exposed to more abuse than windshirts. FYI, you can find unlined runner and warm-up style pants by Nike, Brooks and others in the 6-7oz range. They are a couple ounces heavier than ones by Patagonia, Montane, or Mont Bell, but are much more durable. You can buy them on the charp in most discounters like Ross and Marshall's and they are commonly found in thrift stores, so you won't mind so much when you shred them.
IMHO, windshirts are never a substitute for a poncho or rain shell, but I use one a lot and it is a core part of my layering system. They make a great combo with a poncho too. I have no problem packing both windshirt and rain gear. Packing both a windshirt and abutton down collared shirt doesn't add up for me. Conversely I don't think a rain shell is a good substitute for a windshirt, with breathability being the issue.