Is RMNP a must for you? The Rocky Mountains in Colorado include multiple mountain ranges once you travel west of I-25. With the limitations of the timed entry permit system in RMNP and you being way late to book those permits, I would limit your time there (if at all) to driving and exploring the many overlooks and short trails along Trail Ridge Road. From Boulder, you are about an hour from the RMNP Fall River Entrance. You could leave early from Boulder and get to the Fall River Entrance before 9 am when a timed entry permit is not needed. Drive and explore Trail Ridge Road on your way to your next destination. It would be too much driving time to make it all the way from Boulder over Trail Ridge Road (with time to explore) to Aspen, but Vail and possibly Glenwood Springs would be doable. See this map.
https://goo.gl/maps/2DmoHvYtZV69JiK6A
The western side of RMNP (Grand Lake side) incurred extensive fire damage from the East Troublesome wildfire in October 2020. There are still areas of the park that remain closed. The North Inlet Trail (mentioned in reply #2) is currently closed as explained at this link.
https://www.nps.gov/romo/learn/fire-information-and-regulations.htm
The downtown area of Grand Lake was spared. You can see the fire perimeter and containment lines on a map here.
https://inciweb.nwcg.gov/incident/map/7242/0/111067
I am not sure of your exact timing for the third week of June. Be aware that the FIBArk Festival is in Salida June 17-20 and another poster commented that lodging during that time was heavily booked in Buena Vista and Salida already.
https://www.fibark.com/