I'm with you on the Houdini plus fleece. I've used a Marmot Precip jacket which is pretty much a cheaper version of the Minimalist and the same weight class. Using a fleece mid-layer lets you vary the fleece to suit the season and conditions too.
A GoLite poncho gives a 7oz rain option and you could throw that on top of the bivy if you wanted quick and dirty hail protection, or rig it as a lean-to or a-frame shelter over the bivy for more protection, cooking and changing clothing. You get a pack cover too. A poncho works great with the Houdini for arm and side protection. I'm carrying the poncho for day hiking CYA rain gear and emergency shelter.
I'm without a decent light rain jacket at the moment. I got a deal on an REI Taku, which is darn heavy at 26oz, but it sure works for all day cruddy weather. I've got a Red Ledge microporous PU coated jacket that is 13oz and makes a cheap CYA jacket vs. the poncho. It is well ventilated, but I wouldn't relish spending long hours in PNW drizzle wearing it.
I think rain gear choices should consider the hours of use. I could see using the 7oz wonders for short rain showers and to check off the rain gear box on the list for use in drier climates-- a kind of high quality DriDucks really. But the lack of ventilation features a well as durability and cost issues make me doubtful about walking switchbacks in them for 12 hours at a time. Having effective, durable rain gear really changes the game when hiking in temperate coastal rain forests, extending the hiking season and getting down to life saving gear in many situations. I could spend as much time in my rain shell on a 3 day trip as someone in the Rockies might in a month.
With all that time in a rain shell, the base and mid-layers need to be excellent at moisture transfer yet not be too warm. Hiking uphill in 45F-50F weather with light rain and 85% humidity needs excellent moisture management, but you don't get cold until you stop, or perhaps on exposed level traverses and downhill sections. Often, you find yourself making the choice between wet from sweat or rain and it's not going to be an hour long thing--- it could be all day or DAYS. If I'm wearing a jacket, the front and any vents are open unless there is a real shower. You still have all the area trapped by your suspension that doesn't vent well. A windshirt can be okay on those days with sporadic misty drizzle, but the hours take their toll, and I'd rather use the poncho of the windshirt is going to wet through.
The windshirt/fleece/poncho combo allows for a lot of ventilation and layering options. With my pack covered, it is dry when I take off my rain gear and strip down to base layer. If you hike with a jacket, the rain stops, you take the jacket off and don your pack that has a cold wet suspension-- YUMMY! In extreme downpours, I have sat it out a the base of a tree, with my pack sitting between my legs and the poncho over all. When the deluge lets up, you can shake off the excess and be dry from head to toe, as well as your gear.