What will happen to the property that is 70 years old? Will the entire building be restructured or do buildings generally last more than that?
A really really good question.
Houses are on their own block are safe as you've got the land, and there may be the possibility of subdivisions. You can easily monitor the house's condition, are in control of repairs and onsell as a development proposition if you don't feel like demolishing/rebuilding yourself.
Single storey units in small groups are solid, cheap to maintain, have good land component and only have a small number of owners in the body corp, so are fairly robust. Less flexibility with what you can do, but again you can tell if it's going to fall down and have time to sell up before it becomes uninhabitable.
But you have to wonder about the longevity of some of our high-rises in say 100 - 200 years time. And even sooner for cheaply built residential towers - some of which have been knocked down only 40 years after construction due to high heating costs and social problems. And what about concrete cancer and/or water damage?
You're really betting that the land will be worth so much more that it doesn't matter even if the building has to be knocked over. And a layperson can't really check the building health of a high-rise as readily as they could a single storey house.
Most would have an investing timeframe of 30- 60 years max, rather than 100 years plus, but still I do think that high rise = high risk if major building works are involved and it's much more than just plonking on a project home or townhouses. The cashflow (after costs) had better be good to compensate, and you don't really have control unless you own the whole block.