Yes, this topic surfaces regularly. We are in our ninth year of fulltiming with over 100,000 miles traveled. Most State and Federal parks are no longer issues. Most have 'updated' their parks to meet the larger rigs. That said, most have NOT UPDATED their web pages. There are trade offs to everything. The extra room and CCC of a larger coach, IMO outweighs the reduction of available camp sites. Yellowstone was mentioned. How often will you be going to Yellowstone? Do you NEED to stay INSIDE the park? There are so many camping options available near any of the State or Federal parks you'll come to appreciate a larger coach. As Ivylog mentions, buy as large a coach as you can afford because replacing a too small coach gets expensive. Also, most often, the determining factor is not the size of the camping spot. It's the roads and turns that you'll have to maneuver that limits where you can go. If you can't GET TO the campsite, it won't matter how long it is. Finally, with a larger coach, you'll learn to call ahead to verify if you'll fit. Fortunately, most park rangers are better equipped to be accurate as to whether you'll fit than many private park phone people.
If you want an example, we spent two months at Folsom Lake last year. We are 45' plus the tow. Wanted 50amp service and full hookups. Below is the info from the California State Parks website. Max length listed 31'. They have one pull thru site that's at least 70' long.....Dennis
Folsom Lake Recreation Area