Hmm, so you have the driveway to the south, the neighbor to the west, and the wall to the east. Orientation-wise, that's not exactly optimal. For me, it would also depend on what "below the standard land value" means for you. For us, the standard land value is €850/sqm. For 730sqm, that would be €620,000. Even half the standard land value would be too much for the plot for me. But of course, everyone has to decide that individually. Regarding the trellis, I can't imagine that would work for ivy, for example. My parents had their garage wall covered with it (actually with a trellis), but it was still all over the wall. Afterward, you could still be liable if something happens to their house. I also know knotweed and bindweed for facade greening, but whether the facade would remain intact would probably require good research. The safest would be tall trees, but then it takes years.