There was a period of roughly a month where there was no new snowfall at all in the Placer Creek Valley. Which is something that doesn't happen very often! The snowmachines packed the river trail down very well, and the bike ride out to Spencer Glacier was soooo easy! The entire thing could have been done in 3 hours roundtrip, if we hadn't stopped at the ice to look around.
From the Placer Creek bridge trailhead, you simply follow the snowmachine tracks up the river. This likely requires a January or later time period, as there tend to be open hazards along the creek early on in the winter. Follow the Placer Creek up 10 miles to where it goes under the large railroad bridge, and keep following up until Spencer Glacier!
If there's a lot of snow, skiing should be fine. There were lots of windy days, and I had figured the area would be scoured and full of sastrugi, but the trail was packed, and the snow on the side was soft and plentiful.
It's worth noting: the glacier calves directly into the lake. Meaning, the iceburgs at the front of the glacier are suspended entirely by ice that may only be 2-3 feet thick. They could shift at any moment, so ask yourself if the risk is worth the spelunking experience!
In just the last 2 years, the glacier has receded a solid 200 feet. Where there used to be 60 foot tall blocks of ice, there is bare ground on the sides. It's so bizarre to see.