Having recently gone with my Parents to test out the 500 as a replacement for our 9 year old Renault Laguna i'd have to agree that if you want to take more than two adults in the car on a regular basis the 500 won't be the best option.
We're all fairly short (all under 5ft11 tall) and it was OK with 4 of us in there, but i wouldn't wanna be in the back for more than 20 mins without getting out for a break & an accident wouldn't be pretty.
Apart from the size issue the Parents loved it, we tried a 1.2 Lounge Convertible & a TwinAir Pop Hatch. Of the two the Convertible was the fave. The handling felt more secure as a passenger and (according to Dad) as a driver. It also felt abit better for headroom even with roof up and the 1.2 engine was alot quieter. I dunno if the TA we tried was a rogue one but to me it sounded way too loud.
When you factor in what Fiat are charging for them now we just couldn't justify the compromises so after much deliberating we've decided to look at a Punto Evo and a Renault Clio, both of which have pretty decent offers on them currently.
The new Yaris isn't rated that highly i didn't think. Having driven one i thought it was OK but lacked any wow factor, and although reliability might be better in the Toyota i actually think some of the plastics feel nicer in the Fiat (and Renault). With Fiat if you get a good dealer then i think that's half the battle. We seem to have found one, albeit over an hours drive away in Warwick. Give the Evo a try for size & see if that suits.