When going through RMNP a lesser known but very cool thing to do is drive up Old Fall River Road. It's poorly marked in Google maps - set your GPS for 40.4054, -105.6252. It's marked as an unimproved road but it's easily passable in most passenger cars. It goes by a lot of the major attractions like the Alluvial Fan, Chasm Falls, etc. (pay attention for all the turnouts - if they're packed, there's a reason). Before your trip, Guide to Old Fall River Road
https://rmconservancy.org/product/guide-old-fall-river-road/ is $2 well spent. They usually have printout summaries in a small stand before the start of the road but they run out fast. It tells you the mile markers where you can look for cool things, plus the road's history. Then you end up at the Alpine Visitor's Center (which you probably want to see anyway) and you can take the regular road back. (Note: this is a one way road! You must start at the bottom where that marker is.)
Also for RMNP get the RMNP Afield mobile app for your phone. It works offline and has all the attractions in the park mapped out with background info on them. Cell service is very poor/nonexistent in most of the Park.
If you spend any time in Boulder, in addition to farting around in town, drive up Flagstaff Road a ways. You'll not only see some cool scenery (best views of the Flatirons) you can also stop at Realization Point for a cool 1-hour stroll around with some nice views of the valley. If you time it so you come down just as the sun is setting, Boulder's lights are spectacular.
On the way INTO Boulder don't miss the scenic overlook on Rte 36 at 39.96784, -105.186282. It's a quick easy stop off the road with a view of all of Boulder and the Flatirons. Great photo op.
I'll let others comment on the other spots.