I also tried to use the pregnancy trick, but even the one or two household with 3 kids (thanks to childrens music) didn't move, even after the baby's grew up to todlers.
I had one werewolf do all the hunting all the time. The other sim (I can't remember right know if he was a werewolf too or not, he was in a few testing files, but not in other testing files) I used to get to know all the sims in the town and to get as much people (in the more expensive houses) pregnant as possible, I then had them over for a party and played children's music. I also had my sim get fertility treatment as a LTR.
After my werewolf found some tiberium the cashflow went sky high (I sold them after they grew and had around 6 milion in cash by the end of the two weeks and stoped hunting on wednesday of week 2 as I had more then enough cash to buy all the houses if they would become available), using the gemcutter from supernatural is a huge moneymaker. I started in Sunset Valley in the cheapest home and didn't move until the last day just after midnight. There are two homes in Sunset Valley who are worth exactly the same. I started a fire in one of them (I learned in a practice file that it makes the house worth less, so I could move then to the home that used to be exaclty the same, but was now a couple of dollars more expensive.
I too noticed that the first house was worth a lot more because of the tiberium growing, but that resolved when I sold them. I did need to try to destroy a small part of the yard where the tiberium used to grow to correct the housevallue (just as _Annika_), but as I didn't stay in the other houses longer then it took to make a new phonecall, I didn't had that problem there.
As I only moved on the last day, non of the houses lost any value. I am happy with my score as it was, I only could have gotten an better score if the sims in the more expensive houses would move, but they didn't.
Femke82