Synthetic oil is fully compatible with conventional oil, and there is no reason why you could not switch back to conventional. With high mileage vehicles, there is concern in switching from conventional to synthetic, because synthetic will clean up your oil system and potentially cause seals to leak. But with an '07, you don't have to worry about this.
In general, synthetic oils offer better protection against thermal an oxidative breakdown, and generally let you extend your oil change. If you really want to know where your oil stands, stretch your interval and get an oil analysis done (with TBN). All oil "looks" about the same coming out of your engine, the only real way to know is to have it analyzed by a lab. About $30.
Is synthetic worth it? I plan on keeping my '05 for the long haul, so I think the extra is worth it. If you're going to get rid of the truck in 3-5 years, then it's probably not. Your choice.
I run Mobil 1 10W-30 (synthetic) on 6,000 mile oil changes. My last oil analysis shows I could probably push it to 7,500 miles if I wanted. I bought oil last weekend and for 5 qt it was $23 for Mobil 1, $14 for average conventional. An extra $18 per year, yeah, it's worth it.