Ah, thank you both for your replies.
Aye, though it seems I've also forgotten the broader name (LOD) for the more specific version. But it shouldn't matter too much I guess. Such level-of-detail is pretty standard with most engines nowadays, but I'm already going to use really low-polygon objects anyway.
The only problem I can really think of with the wall-walking is strange angles possibly knocking them off. I'll experiment a bit.
That scene editor looks like it will be really useful! I shall download it as soon as I get home!
Thanks again!