Prima facie this appears plausible; ie buy something of wide appeal, and you won't be short of tenants or buyers.
But what about the evidence?
Luckily it's fairly easy to test this. Identify the suburbs with high recent migrant concentrations (especially refugees) and those with low migrant concentrations. Then compare capital growth performance between the two.
Melbourne's two areas of high migrant concentrations are the north-west (Footscray - St Albans axis) and the south-east (Clayton - Doveton). Its lowest concentration of migrants are in the leafy north-eastern suburbs (eg around Eltham).
Here's what Domain says about the long-term growth record of suburbs that the sort of people you regard as Middle Australia might shun:
Springvale = 13.6%
Clayton = 13.0%
Doveton = 12.3%
Noble Park = 12.1%
Sunshine = 12%
Dallas = 11.9%
Footscray = 10.7%
St Albans = 10.5%
These are more like your 'Middle Australia'. Each could be considered a lovely suburb. But their growth is hardly shattering.
Mentone 10.7%
Ivanhoe = 10.1%
Eltham = 10.0%
Montmorency = 9.6%
Williamstown = 9.4%
Templestowe = 9.2%
Sandringham = 8.3%
Olinda = 8.1% eg
http://www.domain.com.au/public/suburbprofile.aspx?mode=buy&suburb=Olinda&postcode=3788
I can't predict which suburb will grow fastest, but excluding suburbs based on their ethnic makeup could make one less money not more!