agree with Andrew - don't know much about Crestmead, but marsden is on the go at the moment - I have several house/land or land only packages in the area near the Berrinbah wetlands...there is probably an oversupply to some extent, but they seem to be selling ok. There is a massive light industrial area going in on the other side of the wetlands that some of these developments are hoping to supply.
I guess the main point from the investor side is that there is still a general shortage of rental properties all over brissy so well priced rentals are quite sought after.
Carole park is another nearby area worth a bit of a look - not quite there yet but I know a few larger scale land holders starting to look at carve ups.
the major benefit to these areas, whilst some way from the CBD, is that they are in the GC-Bris corridor and very close to the major arterials - gateway/logan mwy/pac hwy.
be interesting to watch how it all goes...