East Coast late Winter/early Spring:
I love RMNP in Colorado, but in March, the roads crossing the Continental Divide will be closed, limiting you to in and out from either the east side or the west side, and a long drive around to connect the two.
Here in the East, be aware the NPS campgrounds along the Skyline Drive and the Blue Ridge Parkway (BRP) may still be closed in March. The highways themselves may be closed in sections, as snow and ice removal equipment is sparse, as are budgets to operate them. It's not uncommon for late season snows to close short to long segments. The Parkway's NPS website shows live closure information and there are updated recorded messages concerning closures on the telephone number listed there.
If you travel the BRP, Peaks of Otter, as mentioned, is a great stop. We enjoy the NC sections even more, as the highest elevations and most dramatic mountain terrains along the BRP are in NC. The Moses Cone Memorial Park in Blowing Rock, NC features a manor house built by textile magnate Moses Cone in the late 1800s/early 1900s along with a network of 25 miles of landscaped carriage trails through the 3,000 acre estate. Nearby, Grandfather Mountain is the newest addition to the NC state parks system, albeit with the former owners still operating a nice, but expensive, mountain-top concession consisting of a visitor center, museum, short walking trails, and the popular "Mile High Swinging Bridge", a pedestrian suspension bridge over a 200' deep ravine, so named because the bridge itself is at 5,280' elevation. The BRP between Blowing Rock/Moses Cone traces the south slope of Grandfather Mountain, and on a clear day, the skyline of Charlotte, NC is visible with binoculars, over 100 miles away.
The BRP between Blowing Rock and Asheville is our favorite segment. It's around 100 miles in length and includes Grandfather Mountain, Linville Falls, the orchards at Altamont Pass, Mount Mitchell (a drive-up to the highest point east of the Mississippi River), Craggy Gardens, and Asheville. One could easily spend a couple or three days exploring the BRP and nearby communities in NC.
Be aware that March will find the Blue Ridge Mountains still in their winter dress of bare, gray trees as far as you can see. The NC section doesn't green up until very late April/early May. You are also likely to experience sub-freezing overnight lows, and the NF and NP campgrounds are likely to be closed. It is also possible to experience bluebird days with highs in the 60s and 70s.
We much enjoy the Charlottesville, VA area (where my wife grew up and where we met in the 1970s), and the nearby Shenandoah Valley can be spectacular in the Spring. On the western side of "The Valley" are the Alleghany Mountains, long narrow sandstone-capped ridges with pastoral valleys in between. The communities of Hot Springs and Warm Springs, VA offer ultra-high end (Hot Springs) and more rustic (Warm Springs) settings. At Warm Springs, the Jefferson Pools offer a natural hot spring soak within one of two historic octagonal structures. At the Jefferson Pools, "historic" is often equated with "dilapidated", but for those who like the idea of soaking in stone-lined pools inside of structures built in the 1700s and early 1800s, it's pretty nice. We really love the NF campground at Hidden Valley, about 5 miles west of Warm Springs. It's on bottomland along the Jackson River and features a network of walking paths along the river and nearby mountain ridges.
My wife and I (58 and 59) have come to enjoy Hot Springs, NC, near Asheville. Hot Springs is a small village of several hundred residents situated where the Appalachian Trail (AT) crosses the French Broad River. It is also the other of of only two natural hot springs in the East. The Hot Springs Resort includes a large riverside campground and the hot spring pools themselves, each on the edge of town, so walking distance from nice restaurants, bars, and shops. The hot spring pools are actually a series of about a dozen Jacuzzi-style tubs into which the 100-102 degree mineral waters are pumped. The pools are streamside, privacy screened except for the water views, and feature overhead heat lamps for cold weather soaking. They rent by the hour and you can take your own beverages of choice. The AT runs directly along Main Street, and March/April sees the arrival of dozens of early-start "thru-hikers" who have survived and conquered the Great Smoky Mountains just to the south in order to reach the first real town since starting their treks some 3-4 weeks earlier. They can be a raucous bunch and fun to be around, especially after they get their first showers and clean clothes in nearly a month.
For us motorheads, not much can beat the spectacles of the Spring NASCAR races at Bristol, TN and Talladega, AL. Check the 2015 NASCAR schedules for dates. In particular, Bristol is a must-see. It reminds you of a football stadium on steroids--seating 160,000 in a man-made bowl over 10 stories high surrounding a concrete-surfaced teacup. Down at Talladega, the Cheaha Mountain Drive is a mini-BRP along the crest of Alabama's highest elevations, including Cheaha Mountain, a drive-up including a stone tower at the summit and several short walking trails to rock outcrop views. With its elevations down in the 2,000-2,500' range, it's much warmer and greener down there in March-April, too. Most motorheads enjoy a day in the area north of Charlotte, NC, where nearly all of the race teams are headquartered. Tours of their facilities, most of them free of charge, give a great look at the engineering and fabrication operations required to produce race cars, and gives us an idea of the enormous amounts of money required to do so.
Towards the southern end of the BRP, and right where it crosses I-40, Asheville NC is a very nice place for dining, shopping, touring the (rather expensive) Biltmore House, and sampling the local brews in what has become the "Brewing Capital of the East". Asheville is nice, perhaps a bit "la-de-da" for those with more rustic sensibilities, but it can be an attractive offering for many of our ladies.
In the lower elevation Piedmont and Coastal Plain regions, April brings many dogwood and azalea festivals. Those in Wilmington, Charleston, and Savannah come to mind, but your 2011 loop included much of that territory.
I hope you enjoy planning and taking your cross-country trip this coming Spring.
Foy