Colorado's a blast! Here's a suggested itinerary
My riding background is similar to yours -- lots of 100-150 mile riding and the occasional long weekend. Last week I did the West coast version of your ride, from L.A. to Denver and back, on a similar bike - a BMW R1100 RT.
The 500 mile days you're talking about are definitely do-able for a "novice" distance rider on a sport-tourer like the Concours. Most of my route in between California and Colorado was desert, so I toughed it out and did 1000 mile days on the ride out and back. I'm 45, and of average health and (un)fitness, and while it was a little arduous, I was back on the bike the next day.
The IronButtAssoc tips are spot on. Stopping every hour for a quick stretch definitely makes a difference. Allow for these breaks in your trip-planning. On the road, I was averaging 80'ish. But with the stops, my average speed for the day was 65mph. And definitely wear earplugs. Ten hours of riding without earplugs, and your ears will be ringing the rest of the day.
Interstates 40 and 70 are fine in a car, but they're miserable on a bike - especially through Arizona and Utah where the temperatures will be in the triple digits this time of year. For your ride, I'd recommend --
Day 1 - Arizona to Durango, Colorado.
Get to Flagstaff from wherever you're picking up the bike, then ride north on 89 and west on 160 to Durango Colorado. This would make a good 1-day ride from most anywhere in Arizona. There are several hours of desert between Flagstaff and Colorado, so I'd recommend leaving Flagstaff no later than 9am. If you've never been to the Grand Canyon, it's only a short detour. Turn north at Williams (30 miles west of Flagstaff) and it will only add about 30 miles to your ride. Time it to be there around sunrise for a spectacular view, and you'll still get across the desert before noon. You might want to make a slight detour to pass through Monument Valley -- but be sure not to miss the photo-op at Four-Corners. If you got an early start and you arrive in Colorado mid-day, spend the afternoon at Mesa Verde National Park viewing the cliff dwellings. It's especially impressive in the late afternoon sun, so you'll have time to get a room and clean up first. Durango is an 1800's mining town something of a tourist destination, so just walk down the main street and take your pick of the many restraunts available. You'll see lots of bikers in Durango - but mostly Harleys (and mostly Rubbies). You'll also see a bizarre paradox in Durango -- notice that every bicyclist you see will be wearing a helmet, while every Harley rider will not. Are bicyles more dangerous than Harleys? Or do bicyclists just value their brains more than Harley riders do?
I was doing 80-90mph on I-40, and pretty much going with the flow of traffice. But watch your speed while riding through the Indian Reservations - speeding tickets are a key source of revenue.
**WARNING** spend the first day getting VERY familiar with the bike's handling - in Colorado you'll be riding mountain roads where an overshot corner could mean a thousand foot drop before the first bounce! The Connie was made for twisties, but the ride is VERY different from your Vulcan. KNOW your bike before you get throttle happy in the mountains. The Connie is quick and nimble. But get in over your head on some of the roads in Colorado, and quite simply, you will die.
Day2 - Durango to Denver -
Twisty mountain roads that were made-to-order for the Connie. Take the 550 north to the 50 east to the 285 north to Denver. Get off bike and attempt to remove stupid grin from face. The entire ride is mountain pass after mountain pass, with the occasional flat stretch tossed in just to keep it interesting

. Keep an eye on your mirror for great photo-ops on the climb out of Durango and down into Ouray. I did this ride in 9 hours, but with lots of photo stops on the way.
If you're not too tired when you get to Denver, consider going to Casa Bonita. Featured in a SouthPark episode, it's this amazing, bizarre, Dali-esque mexican restaurant with flame jugglers, cliff divers and mining tunnels -- all *inside* the restaurant! The food is terrible, but it's worth it for the experience. If Walt Disney built a restaurant instead of a theme park, it would be Casa Bonita.
The State Troopers in Colorado drive grey stealth-mobiles and are plentiful. But I was told by a local bike shop owner that most of the Troopers are riders and are bike-friendly. For my part, I rode 10-20mph over the limit most of the time, and never had a Trooper give me a second look. Just keep it under the limit going through the small towns.
Colorado is prone to summer thunder storms. If your jacket isn't waterproof, pack at least a rain jacket. And if you find a thunderhead brewing while your in a high mountain meadow, find some cover -- your tires will NOT insulate you from lightning (
www.crh.noaa.gov/pub/ltg/ltg_24aug03_parkcnty_biker_fatal.php )
If you've got extra time, I'd spend it touring through Colorado. The Connie will eat up the mountain roads and pretty much any road other than the 70 and the 25 will be twisty.
Day 3-4 -- Prairie grass and Corn fields
The next two days are mile after mile of prairie grass and corn fields. You'll defnitely be wanting a ThrottleRocker or a VistaCruise for this stretch! Take the 75 out of Denver and pick up the 80 in Nebraska. Try to ignore how slowly the clock is moving. If you're not in a hurry, you can ride the Lincoln Highway for a more scenic route (
www.lincolnhighwayassoc.org). It's the northern equivalent of old Route 66 and it roughly parallels the I-80.
Day 5 -- Home again, home again, jiggity-jig
At this point, your in your own back yard and can choose your own route.
The Connie's got great luggage. Pack your gear in two small gym-bag sized duffels for easy packing in the saddle bags. I'd definitely recommend a tank bag - perfect for glasses, cell phone, chapstick (trust me, you'll want it), maps, water, etc. In the mountains, the ride will be plenty to keep your attention. But for the long hours through the plains, music is a definite plus. Either put speakers in your helmet, or use something like the Etymotics ER6. The easiest solution is *noise-attenuating* earplugs (not just the earbuds that came with the player) and an iPod or other mp3 player tucked in your jacket pocket.
Hmmm-- after writing about it, I'm ready to do it again. When are you going?
