What I think, tinted with a bit of personal experience of it.
1. Remember CLOB. - this is the country where they happy happy declare that Singaporean investments all 'bo pakeh' (don't count).
2. Johore is a big place - everywhere can be opened up for development. Esp. true for the suburbs where there is no real focal point for business/activities to push up prices. So why I want to buy your old place when developer can develop an new one right next to yours.
3. Look at it as a place to stay (not earn) - then again 'maybe' because of #1. So my few cents, its safer if you have a 'M'sian connection' (eg. spouse who is m'sian; m'sian close relations; somehow can be 'm'sian' via proxy )
4. Someone said - 'Chinese Tsunami' ...
5. M'sia can build, cannot maintain. - Just go around Johore, examples abound. The condos are the worst.
6. Crime - Break-ins, common enough. Imagine if you are the only one with 'Sgp' car license plate parked outside during weekends. If I am the robber looking out for a house to break in or rob, who you think I go for.
A house is also far easier to break in (esp. when you are not in during weekdays).
An estate with security is a bit better.
Better have someone stay in the house even during weekdays too.
But everybody's 'abacus' calculate differently,
so these are just my few cents on it.