Now that the dollar has risen again, it is the ideal time to buy those addons from overseas, especially those that use the US$. If, like me, the last time you looked at addons the NZ$ was around US71 cents, then now that its at 81 cents you're looking at about a 14% saving.
However there are also big savings for those stores who use Euros, which includes SimMarket. My own scenery on SimMarket has dropped by about 10% when converted to NZ dollars, so get stuck in.