I did not respond to this initially, but I really feel the OP is getting a bad rap here.
Let's be honest: these kinds of party gigs are not the be-all and end-all of career-makers, they usually don't pay that much, and they're an IDEAL opportunity for an advanced student or just-starting-out singer to sing some arias and pocket a little pin money. These are typical "paying-your-dues" gigs, IMO.
THEREFORE... I seriously don't think any offense was intended, simply an assumption made that more established and likely older singers wouldn't be interested in this kind of a gig.
Unfortunately, responding to the original post somehwat aggressively means these types of quickie jobs probably won't get openly posted. And then singers will be frustrated that they never hear about these potential giglets.
So, can we all just try to keep this in perspective? I know the musical world is crashing around our ears (believe me, I know this better than many since I seem to be lying underneath a great deal of operatic rubbble just at the moment, and I'm not seeing signs of a rescue squad yet) but I don't see any point in biting hands that are trying to feed us, even if they're looking to feed a starving student instead of a starving mature artist. It's all good.
*****************************************
"If you only look at what you left behind youll never be able to focus on what lies ahead." - Gusteau