I have to disagree with a couple of things here.
The "warm when wet" idea is more than a bit misleading. During a sleeping bag review years ago, I decided to test the concept, and soaked a North Face Polarguard bag, then wrung it out thoroughly and tried it. Was it warmer than a down bag would have been in the same situation? Undoubtedly. Was it anything approaching fun (or "warm") to be in? Nope. Don't count on being toasty if you get your synthetic sleeping bag wet. If your tent leaks, it means you need a better tent. And modern waterproof shell fabrics shrug off minor drips and puddles anyway. I always seal the seams on my bags, rendering them even further resistant to spills or leaks.
My point is, any sleeping bag needs to be kept dry to function properly. One theoretical exception is in conditions of persistent high humidity, such as for sailing or sea kayaking, where the performance of down can degrade somewhat on a long trip. Nevertheless, I used my down bags while guiding sea kayaking trips and never had a problem. They ride in waterproof stuff sacks anyway.
Synthetic bags are not cheaper - period. A good down bag will far outlast any synthetic sleeping bag. The only partial exception to that is a synthetic bag that never is compressed for travel. A Butler Bag, for example, hardly compresses at all when you roll it up, so I expect mine to last a good long while. Any of the big base-camp style bags are similar. But any synthetic bag that you have to stuff to carry will last a fraction as long as a down bag before its performance has degraded significantly. The investment really pays off.