I live here in Mill Valley and agree that Mill Valley is both nicer and more central to those things you want to do. I am biased being a native Marinite, but I agree with Tallymom, this place is very gorgeous -- and I will try to entice you further with some of my favorite local things to do here.
During non-rush hours, SF is only about 15 minute drive south of here + a five-dollar toll to cross the golden gate bridge (I know, ridiculous), wine country is about an hour north, and Muir Woods and the ocean are both on the same road out of town -- 15 minute drive only because the road is very twisty (Muir Beach is just a couple minutes down the road from Muir Woods parking lot -- you can actually hike between the two easily enough, if you want to visit the beach on the same day as you roam among the redwoods).
Point Reyes is also close too, depending how you want to go and what part you want to visit (its a pretty big place). If you are bent on going to the light house in the North, the fastest path is probably a forty+ minute drive (101 north, to Sir Francis Drake East). Alternatively, you can take the path me and my sister take, when she visits. We just love taking the afternoon/evening to drive the road over Mt. Tam and go by Muir Woods, then travel through all the tiny West Marin towns -- Muir Beach, Stinson Beach, Bolinas, Olema, Dogtown, Point Reyes Station, and Inverness....sight-seeing and catching up with each other's lives, buying coffee & goodies, and eating at some of the out of the way resturants out there (there are several to choose from -- I recommend Bolinas' outdoor cafe downtown and in Inverness this little Czech resturant called Vladamir's) as we go. This path takes longer (again twisty and small road) and we make a lot of stops all along the way -- but its absolutely gorgeous country road, incredibly relaxing, not crowded with tourists at all, and it does go toward North Point Reyes and to the Point Reyes Lighthouse if thats your goal (
http://www.nps.gov/pore/planyourvisit/hours.htm).
If you aren't tired yet, you can then continue up into Wine County from here as well. On the way to wine country from Point Reyes, I recommend you take the Petaluma-Pt. Reyes road and visit another neat little place, especially if you like stinky French cheese, called the Cheese Factory. It makes one of the best (award winning) domestic Brie, Camembert, and a little known, limburger-ish cheese called Schloss that, if you are a cheese fanatic like me, you will greatly enjoy. If you want to spend a little time here (it is a little picnic area with a duck pond, etc. to picnic or simply relax next to) you can even take a tour of the cheese factory itself (I think its still free --
http://www.marinfrenchcheese.com/).
Then continue east to Petaluma and then to Napa for Wine tasting, but all that might make a really long day for me. You might want to spend the night somewhere in Sonoma or Napa and break this drive up into two days. You then zip back on the 101 freeway to Mill Valley when you are done.
If you want a more localized option for Pt. Reyes you can also just go to Bolinas from Mill Valley for breakfast, then go out Mesa Road (unpaved near end) to the Palomarin trail head and park there and hike all over the southern spur of Point Reyes (which, for hiking, is my personal favorite part of Point Reyes). It has the ocean/beach a short 1o minute hike away, and lots of wildlife all over. This Bolinas trip to Point Reyes is all near Mill Valley, about half hour a way, and you can hike as much as you want then come back to your lodgings anytime you want and go onto something else.
If you are a nature nut, you may want to put Audubon Canyon Ranch (
http://www.egret.org/bolinas_when.html) on your itinerary as well (make reservations to visit) and go see the nesting grounds for the great blue heron and snowy egrets. Its right on the way to Bolinas and it has a neat little hiking loop to an overlooking bluff to their nesting grounds of these rare and endangered birds.
Santa Cruz and Monterey are pretty far away from Mill Valley (i.e. I would guess 3 hours one way to Monterey) and will chew up a lot of your time in driving if you are planning to go there for only an afternoon. If you want to go there still, I would spend a night or two down there as well.
Okay, that's enough of a travel endorsement for Marin, I think. I hope it helps. I could easily spend an entire week in Mill Valley/Marin, or SF, or wine country as it is...doing all three in a week might make my head explode. I admire your stamina!