I have been probably 5 times (we live in CO and do it every few years).

3 days is perfect. Plan a day or even two at the hot springs.

A day in Aspen is fun, tons of hikes in and around aspen. Aspens is pricey though so be prepared for that.

Hanging Lake is probably your best bet for a fun hike near glenwood. It requires a reservation nowadays though, but worth it. Super fun, not too hard, and water is beautiful.