You need over 10,000 posts to have sparkling stars :).
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Sounds like a good idea.
Putting this into perspective:
There are 288 VIPs in total.
There are two platinum members with full sets (going by MAD's 10,000 comment).
An animation for the 288 versus the animation for the 2 would put so much server lag into place. Hollywood was saying "Server lag pfft whatever" but would you like for the future to always have that "Server is Busy" message come up? No, you'd rather faster page loads etc.
The thing is, it would be a huge strain, and the reason we can do it for full sets of platinum stars is that there are like 2 users (who haven't been banned) that got that far ;) Of course the banned users don't get the stars.
That's probably why it wouldn't work. But you do have the green light flashing for online/offline? Also I don't think there's any way for userpips to blink based on offline/online, it would just have to blink 24/7.
Considering the user on/offline you stated, you could pull the get string from the code for that to display "image 1" if online and then "image two" while offline much alike the on/offline image. :]