Hi Babushka
I wouldn't take too much notice of vacancy rates on sites like this as they can be inaccurate. Far better to hop on the major websites (realestate and Domain) and look to see what's renting at the moment. Local papers are also a good indicator of demand and the Hills Shire Times is down to 3 pages of rentals, as opposed to 6-7 pages 4 yrs ago
Changing times....
I can tell you that houses rent generally very well in most of those suburbs, though better in Castle Hill as its more central and accessible to transport, shops etc. Your definition of "newish" will need refining, however, if you're going to consider CH, however, as it's an older suburb and most new rebuilds are over your budget. Nothing wrong with older houses, as long as they've been maintained, and depreciation can be almost as good. Big advantage, of course, with older stock, is the land size tends to be larger (think 800sqm as opposed to 500sqm). Ditto Pennant Hills, though you will be able to pick up a townhouse or smaller dwelling for your money here- PH does have the advantage of rail too.
Rouse Hill and Kellyville have exploded in growth over the last 5 yrs in particular, and there are pockets that are more isolated than others, which I wouldn't buy in. You do really need to know the area (dedicate some serious time to exploring and driving around the area, talking to agents, other investors etc) before investing as there are wide diversities in prices depending on where you're looking. There's been a plethora of new housing built in this area, some of it bordering nearby Stanhope Gardens (eg Ponds estate) but all are not equal. Stick to the Castle Hill side (near Kellyville Plaza) for the best value for money, in my opinion, and look out for quality of builds as these can vary widely as well. Consider proximity to transport and shops, schools and parks as most tenants in these areas are families with young children who want to be close to some, if not all, of these amenities.
You won't have any problems renting in any of these areas, though returns will vary, again depending on location and type of house. Expect to get around 4.5-5% as a general rule.
Current examples include:
CH house worth approx $900K in CH renting $850 p/wk = 4.9%
Kellyville house recent price $650K renting $600 p/wk= 4.8%
Hope this helps- I know these areas extremely well as well as the agents that sell in them. There's good, bad and ugly out there so do your DD and good luck!