I've started to think about Frankston from another perspective. We've lived in the south east for 17 years (Berwick) I'm not saying Frankston won't go up but the median price is currently not far below Berwick which is ridiculous, the median simply can't go above these suburbs. It's a dive in comparison (it doesn't even compare to Narre Warren for that matter), and the difference in infrastructure between the Pakenham Corridor and Frankston corridor is also beyond huge.
Area's in Frankston west of the peninsula freeway have shot up to 330k-350k that were around 250k only a couple years ago so the people who bought in these areas have done very well imo.
For the type of house in Frankston Heights for 380k to 450k you could get a far nicer middle class property in Berwick which although you can't subdivide yet, the quality between properties is huge! It's a far nicer area than Frankston South although not arguably as nice as Mt Eliza. But comparing it to the homes that make up 90% Frankston, Frankston North and Karingal etc isn't possible until you go as far as Tinks Rd.
http://house.ksou.cn/p.php?q=Berwick&sta=vic&id=433641 this is the lowest socioeconomic area in all of Berwick
http://house.ksou.cn/p.php?q=Berwic...&minprice=0&maxprice=450000&minbed=0&maxbed=0
For over 450k I would definitely try to afford west of the rail tracks/Frankston station before considering Berwick, but as far as Frankston Heights, North, inner CBD, Karingal go forget it for the 300k-350k those homes are currently going for you can buy a property in the Timbarra estate for that price!
Just adding my 2 cents