personally i would never ask people to contribute money if we invited them for a meal. but that could be our hospitality background. we often put on spit roasts, luncheons, huge weekender parties - halloween alone costs us about $500 (and that is just the wholesale cost of ingredients)
the only thing i ever ask people to bring is their own alcohol.
if i went to someone's house for dinner and they asked for money when we were leaving i would probably think they were joking. and wouldn't return for dinner the next time.