So...is there ever a good time to call a vampire, or invite them over?

There are a couple work around for this issue. There is a mod over at Mod The Sims that has a mod that will fix this (first check to see if it has been updated for this latest patch), and the other if you have Get Together, form a club and include those you want to invite over. I promise you that they will show up when you start up the club gathering. The cool thing about the club gatherings you can set it up any way you want.