for german property market, you have to have related german words (which is "immobilien") to be able to sell it to german domainers or end users in germany (brokers, agents, etc.).
the only usage of this domain name which comes into my mind is to use it for seo (because of the keywords "buy property") for other markets than german market. i mean to look at it like gTld.
but i don't know how google treats that, considering the .de extension.
re. estibot: yeah, its the best free tool, but still a lot must be improved. for instance in this case, the relation to .de extension is totally left out. estibot probably looks at the good monthly global searches, overture, cpc, etc. and estimates a high value, without considering that such a name is useless for local german market.
anyway, good luck