I was just at Yosemite two weeks ago. Although beautiful still and majestic, the drought has definitely taken its toll. I was told spring is the best time to go. That said, we can't always plan our vacations around when is the best time.
I am TERRIFIED of mountain driving, so we took 140 and it was very easy. We base camped at the KOA in Mariposa/Midpines and drove our Jeep in to Yosemite. It was about 40 minutes in, and the drive is beautiful. I would never drive into Yosemite in the 40-ft RV. But there are PLENTY of big rigs in and out, and there are the huge tour buses in and out all day. However, be aware of your length. There are signs everywhere that say the 45 TOTAL limit vehicle length is enforced. The KOA was very nice. I would stay there again. We also spent a day driving the Jeep up the gold corridor to Jamestown/Sonora and into Columbia. That was amazing! I loved those little old gold towns.
Have a great time!!