Adult-scaled sets at an appropriate adult pocket price-point that also tap in on the nostalgia would be a great place go start. For example, a 200-300 euro large castle (steck, of course), with old fashioned Nuremberg or early-90s knights. Or its Western equivalent. That kind of thing would be awesome.
Or a 250 euro big pirate ship or schooner. Adults do pay those kind of prices for Lego. Apparently, if the Enterprise is amything to go by, they also pay them for Playmobil.
