According to the US Federal Reserve Study of international housing markets, prices in Germany have been falling for 25 years. I have yet to read anything that really convinces me that they are suddenly going to rise now. I also wonder if a stronger economy will cause a cultural shift in the German way of thinking i.e. that renting is better than buying.
I don't think that's really true. Property prices did rise quite a bit sometime around the period 1987 to 1993. Since then prices have been more or less constant in nominal terms (which is a fall in real terms) in the better areas, and falling in not so good areas.
The tax breaks for East German properties in the early to mid 90s was not just for commercial properties, but also residential properties. AFAIK the primary focus was residential properties. This resulted in too much supply. Following (re)unification there was a huge loss of jobs in the east as the companies there could no longer compete once they were forced to pay West German wages. This has resulted in population decline from large parts of Eastern Germany. As a result, these properties built in the 90s are now often worth only about half what was paid for them (personally know someone who lost money on an appartment and is now trying to let it to students). However A few areas in East Germany (mainly Leipzig and to a lesser extent Dresden AFAIK) are doing quite well in terms of economics and job creation.
Some of the old traditional industrial cities in West Germany are also suffering from population decline due to job losses. Typical examples would be Gelsenkirchen and perhaps Essen.
In contrast, cities such as Munich, Stuttgart, Frankfurt and Hamburg, and many smaller cities like Wiesbaden, Darmstadt, Nuernberg etc, are doing well economically. There is strong demand for rental accomodation in many of these cities. However, even here I also find it hard to see much scope for significant capital gains.
Berlin is a law onto itself with its half western, half eastern history. Very high unemployment as most people know. However it is the Federal Capital now and one can expect more civil servants and lobbyists to move there over the next 10 years.
If I was living in Germany I would certainly consider investment there, though I would be wary of Berlin (partially due to the high EA commission of 6 to 7% there). However I think there could be tax problems which make it less economical if you are an irish resident.