The E450 chassis does more than carry more or tow more.
On small Class C motorhomes that don't need the E450 for the above reasons, an E450 gives you bigger brakes for more time between brake jobs, more transmission cooling for less heat load on the engine and longer transmission life, a 4.5 inch wider rear dually stance for better lateral stability offroad and in high side winds, pump boosted power steering instead of vacuum boosted power steering (at least for our model year of the E450), thicker steel in the chassis frame for less frame torsional twisting transfer into the coach box, and lower differential gearing when pulling up long grades for less heat load on the V10 in hot weather.
We considered the long term benefits of the E450 over the E350 as well worth the (relatively) few extra dollars we had to pay for the option when we bought our small Class C. Since we go offroad in the desert with our Class C, we generally feel more secure with the additional chassis ruggedness under us.