Don't quote me exactly but I would guess about 4 miles or so. It is a relatively short ride on the bus. It was a short walk fro the Riu Palace Las Americas.
Will USA Transfers let you stop at a Walmart or similar on the way to the resort for an extra fee or no? That could be an option if you don't want to leave. We have done Xplor in the past but typically we never leave the resort. Way too much fun happening at any given time...don't want to miss it!
Been visiting Cancun and much of the coastal areas of the Yucatan for 20 years and most of that time we never stayed at an all-inclusive resort. We found our own boutique hotels, ventured out at night, and explored at will up and down the coast. That being said, it's always prudent to be aware of ones surroundings, and the only time I ever felt unsafe was when a buddy and I decided it was a good idea to visit a strip bar at 3am on the advice of a taxi driver. Not our best decision! But we survived it although I would not venture that far off the beaten path again, especially with the lovely Stephanie. But have no fear on visiting TTR and the Cancun resort areas you are considering. We're taking our running gear and will be doing 3 or 4 miles every day with no second thoughts. The sidewalks are wide, clean, and safe. Enjoy your trip!