Welcome to TMC! Good first post, much better than mine anyway. There is no doubt that with the distances and elevation gains you're talking about for routes instead of Yosemite Valley, a 60 wouldn't be able to do that without another charging stop somewhere. If someone really wants to drive those kind of distances, they'll need an 85 or wait for more charging instrastructure.
Edit: Dang, GG beat me to the punch. I agree with his post although I thought Yosemite Valley was within reach of Manteca and/or Lathrop even for a 60? It's only 115 miles or so from Manteca to the Ahwahnee Hotel in the middle of the Valley.
Thanks for the kind welcome! I'd think if you take it easy on 120, take Old Priest Grade and keep your speed at or below the park limit (45 mph) you could make it in good to ideal conditions, i.e. limited use of heat/defrost, but you do have to climb to 6,000 feet at Crane Flat before dropping 2,000 feet to the Valley.
Ultimately, they'd need SCs on all four gateway routes. SCs along S.R. 99 at Manteca/Merced/Fresno are too far west for points east of Yosemite Valley, and Manteca and maybe Fresno are pushing it for the Valley owing to the extra 2,000 feet of climb (but you lose it again) compared to 140 from Merced; putting SCs along/near S.R. 49 at Groveland (120), Mariposa (140) and Oakhurst (41), plus Lee Vining (120 East) would provide better coverage, but the problem is usage would be very seasonal, and finding sufficient power might be a problem. And putting SCs inside the park seems problematic, as they're a proprietary standard.
For 120, putting the SC 20 miles east of Manteca at Oakdale would help for the Valley, but I think it might still be marginal going up to the high country. Yosemite Junction 25 miles east of Oakdale would be an ideal location, except AFAIK there's nothing there anymore (there used to be a gas station/ restaurant and tourist info center, but the station/restaurant closed years ago). Groveland is the best location for those going to Yosemite, but not for other routes east of Oakdale.
I suspect the best compromise to serve the widest area would be at Jamestown about 3-5 miles east of Yosemite Junction, either at the Chicken Ranch Casino or else downtown Jamestown. Chicken Ranch would have the power, but would probably want to install HPWCs rather than SCs; after all, they want people to stay awhile. But either location not only covers all of Yosemite (needing just a minor detour), they would also cover 108 past Sonora (Dodge Ridge/Pinecrest, Sonora Pass, and Bridgeport), and 4 via Angel's Camp (Calaveras Big Trees, Mt. Reba/Bear Valley/Lake Alpine, Ebbett's Pass and Markleeville, maybe South Lake Tahoe and Minden).
For the North/South I-5 route, Lodi (I-5 at S.R. 12) is more central between Corning (147 miles) and Harris Ranch (152) miles, although the segments are still a bit long for 60s in less than ideal conditions. You probably need two SCs at about 100 mile intervals, say Woodland and Ingram Canyon Rd. south of Tracy/Vernalis on I-5.