As for the Ready Mix ($199; www.patagonia.com), it's one of two types of soft-shell jackets on the market. In this case, it's sort of a light rainjacketsoft and stretchy, but not entirely waterproof. So it's good for those short downpours you're apt to see in Yosemite. I will say it's also more breathable than most completely rainproof garments, so it might be more comfortable when it's warm.
That said, I admit I don't fully buy into the concept of a rainjacket that isn't really rainproof. I prefer the other evolutionary branch of soft shells, which offer short-term water-repellency along with some insulation. That way they can be combined with a traditional "hard shell" when the weather gets really nasty. So you might also look into a light fully waterproof jacket. Marmot's Essence ($150; www.marmot.com) is one such jacket. It uses Marmot's very good PreCip Plus coating, for a jacket that offers lot of weather-proofness plus modest breathability. Another good choice would be REI's Taku ($199; www.rei.com), which adds some features such as stretch panels and pit zips for better ventilation.
For a little more breathability at a higher price, Arc'teryx's Alpha SL ($250; www.arcteryx.com) is a light jacket made with Gore PacLite, a very breathable material that still offers excellent rain protection. Enough breathability for those times when it's 85 degrees and raining? Um, no. But for all those other times, it's great.
Pick up a copy of the 2006 Outside Buyer's Guide, on newsstands now, for a look at 396 torture-tested products, including the 2006 Gear of the Year award winners and an all-new women-specific review section.