Well, I guess I don't see how showing what someone had done creatively to a stock house would be frivolous, but as I said, it could be done in the context of a contest. Different from build a house to a moderator's specs because the house in general is already built. If you like, I could come up with a challenge with rules etc. for just such a thing. I have personally learned a lot by seeing what others have done to stock houses, and I am endlessly amazed at how poorly set up most stock houses are, let alone how well decorated. I absolutely can see how a thread like that can get out of hand. It can easily become a p-ing contest of mine's bigger/better than yours, which would ruin it. Such threads on other sites have definitely degenerated and become space hogs and boring. My idea was to show what you've done, and say why and how you did it without the use of mods or unacceptable cc. It's up to you guys of course, and I want you to know it was just an idea and won't be a harm to me in anyway if you decide to not allow it.
Landscaping could be another facet or challenge of such a contest and could even help people learn a few things about landscaping. It's really more than plunk down a few trees as I'm sure you know, and I for one would love to learn how to do more with less. I tend to clutter.
I love the way the build a house contest is going at the moment and hope there will be a lot more entries. Each house is so very different and each one is creative, well done and lovely. I'd live in any of them. I'm personally torn between two of them for my favorites and really don't know how, whoever is going to judge them, will do so. Definitely shows a lot of creativity, which is one of the reasons I love Sims.