This is uncanny, as I happened to be in Auburn with a bike earlier this week, and needed to return to Sac. I've otherwise not ridden SacRT light rail in years. The Placer bus took me to Watt/80 station, where I connected onto the Blue line into the city. This was in the early morning, around 8 AM. The bus was early, allowing me to catch the earlier train, which arrived on-time.
From that experience, I'd say solo-rider light rail is perfectly viable if you have a bike to use while in the city, and you're coming in from the suburbs roughly along 80, or along 50. The clincher is getting to that first station, because once you're on the train, it's smooth sailing (unless something locks up the grid).
That SacRT buses (6-ish AM to 9-ish PM) have a narrower schedule than light rail (5 ish AM to midnight) means broken connections late at night or in the early morning, which is a travesty. Placer buses have even narrower hours, with no Sunday service whatsoever.
In my case, I didn't have a car to drive to Sac, and even if I did, needing to bring the bike would complicate things. But I'll admit that it's unlikely I'll find myself in that specific situation again, since my other option was Placer's commuter bus from Auburn, directly into Sac.
I would say light rail adds options, which in this case, I needed and appreciated.