According to Serta's web site:

The all-new Perfect Day mattresses feature Serta's revolutionary iSeries™ technology, combining Serta's finest comfort innovation with our most advanced coil support system."

This tells you a lot. It is a spring bed. It has cooling foam. It should be a good bed. There are better available in different technologies (foam, air, water). Even Serta sells the iComfort line, which in my opinion will outlast this bed.

The best value bed is one that you sleep well on, with minimal tossing and turning, will last for a long time, and is competitively priced. Serta does control retail pricing for this model, so retailers should be offering about the same price.

And yes differences in price, in the same manufacturer's line would indicate either better quality, or more likely more parts. Mattress makers, like most any manufacturer, get about 3 times cost when they wholesale. It would be a rare find that a retailer would sell it for less than it costs.

By pillow top pad versus smooth, do you mean quilted versus non quilted? If that is what your asking, we believe quilted tops provide better ventilation. And therefore a more comfortable nights sleep when it comes to sleep temperature, than the smooth topped ones.

Hope that helps...Sleep Well!