Going by the map, your route from SLC to Boise to Reno is "oh, so boring". I mean really unscenic straight line freeway riding. Everything will be dry with little color.
Ideally I would advise (from SLC) going to Bear Lake, then up to Salmon and back to Boise. Your schedule doesn't allow much deviation.
So, Maybe head straight north on I-15 to Blackfoot.
NW on 26 to Arco. This is a nice ride in the evening. Sagebrush desert past Atomic City. Site of Nuke #1. Who knows what kind of giant ants and spiders are lurking out there. Eat at Pickles and stay at KD's in Arco.
If you have time take hwy 93 to Challis then west on 75 and 21 to Boise. This is one of the best rides in the Northwest.
If time is short, head west, on 93, from Arco, past Crater of the Moon, to hwy 20 to Boise.
If all that is too much, from SLC head west on 50 and north on 93. When 93 divides bear left. That will get you closer to Boise.
After your meet up...From Boise, east on I-84 (you are actually going south quite a bit) to Mt Home, then south on 51 to Elko on I-80.
west a couple miles to Carlin NV and south on 278 to Hwy 50. Now head west to Reno. Eureka has a nice motel. Austin is interesting.
These two lane roads are fast, mostly empty and sagebrush high desert cattle land. 50 is labeled the "Loneliest Road in America", and it is one of the busier roads out here. It follows the Pony Express and Stagecoach routes. Watch your gas out here.
Another option would be...from SLC, west on 50 and north at Eureka to Boise. Then west on I-84 to Baker City, OR and south to John Day then south on 395 to Reno. A very nice ride. Dense forests, cattle lands, and a section of serious desert. Stop at Seneca and visit the bobcat.