Slightly dissatisfied with my Mpg

Your MFD changes if the reset is pressed. I would not count on the number on it at purchase as being lifetime mpg.
Your 49.8 mpg is very good for your described drive. Air conditioning and higher speeds 60's and above drop my mpg noticably. If I drive my touring edition (195/55/16" standard tires) w/air on a hot day and "ignore" good mpg habbits I get 45-48 mpg. With lots of stop and go traffic and hot temps I have even been in the 30's...continue experimenting and you'll see 50's and perhaps even 30's
Part of the joy of owning a Prius is in the control you can gain. The impact can spill over to other vehicles driven but the effect on a Prius is magnified.

 

Pirelli Cinturato P5 tires have crap rolling resistance

Update on this:
I now know something about them. In the July 2010 issue of Consumer Reports, they rated all season tires and one of the attributes they rated was rolling resistasnce. They have their 5 different dot types that range from poor to excellent. The Pirelli Cinturato P5 got the 2nd worst dot, corresponding to fair. So, I'm sure those are hurting your mileage.

A few others in their tests also got fair rolling resistance, but none got poor. The Cinturato P5 and the other ones that got fair ought to go on a don't buy list of tires for Priuses. (I'll type them up when I get some more time.)

The all season tires w/excellent rolling resistance that they tested include the Michelin Energy Saver A/S (which they recommended and gave a #2 in overall score) and the Uniroyal Tiger Paw Tour SR.

Ones that got the next best rolling resistance ratings were (in descending order of overall performance): Cooper GFE, Yokohama Avid Touring S, Cooper Lifeliner GLS, Sumitomo HTR T4.

I guess either the previous owner or the dealer who replaced the tires didn't know what they were doing in terms of picking tires that wouldn't hurt mileage.